Depression

If you have been feeling low in mood and lost interest or pleasure in the things that you typically enjoy, and have been feeling this way for more than a couple of weeks, it is likely that you are feeling depressed. You may feel stuck in patterns of negative thinking and feel hopeless about your situation and the future. You may feel lethargic and struggle to concentrate, making it hard to work or socialise as normal. You may also experience changes in your sleep pattern, appetite and sex drive. You may find yourself dwelling on past events, and even feeling guilty or worthless.

Depression can be mild, moderate or severe. During severe periods of depression, you can feel so hopeless about the future that you experience thoughts of ending your own life or wishing that you were dead. You may feel reasonably confident that despite feeling this way you would never take steps towards ending your own life, for example thinking about your family, friends or faith may give you reasons for staying alive. On the other hand, you may feel that there is nothing to stop you from wanting to end your life - if this is the case, it is extremely important to contact your GP immediately or to seek urgent help elsewhere, for example attending A&E or calling the Samaritans.

Whatever the severity of your depression, it is important to seek help, whether through your GP or seeking a therapist independently.
Your GP can advise you on medication and psychological therapy within the NHS.

Anxiety

You may find yourself worrying a lot and feeling on edge.  
There are many different types of anxiety problem, as described below:

Panic disorder

Recurring and regular panic attacks that seem to come out of the blue.  Panic attacks are typically accompanied by intense bodily sensations, such as a racing heart, chest tightness, rapid breathing, nausea, dizziness/feeling faint, flushes or chills, churning stomach, urge to empty bladder/bowels.  Sometimes we can experience feelings of 'unreality', feeling disconnected or detached from what's going on around us, which can be extremely frightening.  It is quite common to fear that you are about to have a heart attack or a stroke, which can understandably lead to efforts to protect yourself, both in the immediate situation (e.g. lying down, calling an ambulance) and in the longer term (e.g. giving up exercise, avoiding being alone, avoiding situations that may trigger another panic attack).  The fear of having another panic attack can itself lead to intense feelings of anxiety,

Generalised anxiety

Anxiety about a wide range of situations (e.g. work, finances, relationships, health), leading to persistent worry that can feel uncontrollable.  You may even describe yourself a a 'worrier' and have a tendency to worry about all sorts of things, often preparing yourself for the worst possible scenarios.  You may find that a day rarely goes by without worrying and this affects your ability to get on with your day-to-day life.  

Obsessive Compulsive Disorder (OCD)

Obsessions are persistent 'intrusive' thoughts, doubts, images or urges that are experienced as unpleasant and unwanted, often terrifying.  For example, fear of causing harm to oneself or others through one's actions (e.g. spreading contamination, causing an accident, violent or abusive acts, blasphemous or other behaviour felt to be unacceptable and against one's own moral code).  These 'intrusive' experiences are often accompanied by a strong sense of responsibility to prevent harm, which can lead you to feel compelled to engage in efforts to prevent harm, for example persistent checking to avoid mistakes, cleaning to prevent contamination, or 'superstitious' acts (repeating mantras, doing things a certain number of times or a certain way).  These behaviours that are intended to prevent harm or to  protect yourself or others are known as  'compulsions' or 'rituals'.  It is also common to seek reassurance repeatedly when struggling with uncertainty about whether things will be alright.  You may even try to stop the obsessions from coming to mind in the first place, for example trying to block them out or by avoiding situations that trigger them, but frustratingly you may find that this doesn't stop them, and may even be getting them more frequently.

Body dysmorphic disorder (BDD)

Unhappiness with an aspect of appearance and spending a lot of time worrying about it.  You may be convinced that you are 'ugly' and find it hard to believe others when they tell you otherwise.  This can lead to efforts to hide or camouflage this aspect of your appearance, often spending hours getting ready or checking your appearance, or even to avoid other people due to worrying about them noticing.  This can lead to a very restricted life, for example ruling out the possibility of a relationship or limiting your work and social life.  You may spend a lot of time comparing your own appearance to others, checking your appearance in the mirror or may even avoid mirrors altogether.  Your unhappiness with your appearance may even have led you to consider cosmetic surgery.  

Post traumatic stress disorder (PTSD)

Anxiety arising from either experiencing or witnessing a traumatic event (e.g. assault, accident, abuse, natural disaster, military combat), that leaves an ongoing sense of threat, which can lead to feeing as if you are reliving the experience through nightmares or flashbacks, feeling constantly on edge and avoiding anything that reminds you of the traumatic event.

Social anxiety

A persistent fear of social situations, typically due to a fear of failing or looking weak in some way, of being judged negatively by others or perhaps being embarrassed or humiliated.  This can lead to avoidance of the situations we come to dread (e.g. talking to others, whether in individual or group situations, eating in front of others, speaking in meetings, talking on the the phone, making conversation in social situations), making it even harder to face these situations in the future.  Our lives can become very restricted, for example we may base important decisions about work/career choices and rule out the possibility of relationships, have a limited social life due to our fear and avoidance.

Health Anxiety

Persistent worrying about your health, to the extent that worrying about your health has become a problem in its own right.  You may be experiencing symptoms that continue to cause you concern that you may have a serious illness, despite reassurances from your doctor.  It may be that you do not have particular symptoms but find yourself constantly worried about the possibility of becoming seriously ill in the future.  You may find that you constantly seek reassurance from your doctor, seeking frequent medical tests and investigations, or research symptoms on the internet.  Alternatively, you may avoid seeing your GP and avoid other things (e.g. physical exertion, reading about illness or seeing it on the TV). You may find it hard to remain reassured and may find yourself on the alert for bodily changes, to the point that noticing these changes leads to further worrying.

Phobias

Fear of specific objects (e.g. needles), animals (e.g. dogs, spiders, snakes), situations (e.g. dental appointments) or activities (e.g. flying).

Low self-esteem or confidence difficulties

You may find it hard to accept yourself as 'good enough', to be kind to yourself or 'cut yourself some slack' at times of difficulty.  You may struggle to feel that you deserve the good things in life and perhaps find you are your worst critic.  It may be that you have experienced bullying or other experiences that have left you feeling worthless.  There may be echoes of others' voices that keep you feeling bad about yourself.  Alternatively, you may have a strong sense of shame about past events or feelings of guilt and self-blame that are difficult to let go of.  You may find yourself caught in a struggle between your head and heart - despite being able to logically 'know' that things are not your fault, it may be hard to truly 'feel' this in your heart.