1. Depression

Depression consists of multiple symptoms such as low mood/sadness, low self-esteem, hopeless feeling, helpless feeling, feeling guilt-ridden, being irritable or intolerant, being unmotivated, feeling uninterested, feeling as if it's hard to make decisions, difficulty to concentrate, forgetfulness, and takes no enjoyment in life.

During a diagnosis, doctors may run blood tests to rule out any other illnesses that may have the same symptoms of depression.

2. Bipolar Disorder

There are four different bipolar disorders:

Bipolar 1: Severe mania lasting more than a week.

Bipolar 2: Swings between a less severe mania and low mood.

Cyclothymia: Longer term hypomanic and depressive episodes lasting for up to two years.

Unspecified bipolar disorder: Mixture of the three types.

In general, bipolar disorder can make a person have extreme personality changes. The main cause of this illness is an imbalance of chemicals involved in brain function. In order to be diagnosed, you must see a psychiatrist or clinical psychologist. There are also other illnesses that cause mood swings. Just having mood swings does not mean you have bipolar disorder, but it is a possibility.

3. Panic Disorder

During a lifetime, most people experience some kind of panic attack. But having panic disorder is much more serious than that, and it's something that happens on a regular basis. If you have this disorder, then you don't only get panic attacks when you are in fear but also when you are excited. When you start to panic, your body begins a "fight or flight" thinking process due to hormones. Adrenaline goes coursing through your body and you basically begin to "freak out" beyond control. These attacks can be so severe that people may think they are having a heart attack or some other bodily malfunction.

4. Anxiety Disorder

There are multiple types of anxiety disorders, but here are the four most common.

Generalized anxiety disorder: Continuous stress/worry leading to everyday life becoming a threat. People with this disorder have social fears, health worries, fear of disaster, and they are usually perfectionists. This makes it difficult to concentrate and make life decisions. If you have this, you easily become obsessed with things and that can impact your social life. You may want to go to the doctor if you are having these problems for the majority of days in a six-month period of time.

Social anxiety disorder: Excessive nerves and dread of social situations are the two main symptoms of this kind of anxiety. You may be extremely self-conscious and worried about others judging you at all times. Most people experience this at one time or another, but it can truly take a toll on your everyday life and most important relationships. It leads to isolation and depression, over-rehearsal of conversations or meetings, and over planning.

Separation anxiety disorder: This disorder usually develops in children, but it can follow you to adulthood. Separation anxiety takes place when a child is taken from its mother/father/guardian because they lose a feeling of safety. It coincides with a fear of being alone or forgotten about if you are separated for too long.

Obsessive-compulsive disorder: OCD comes along with extreme excessive and uncontrollable thoughts. Most people relate it to cleaning, but you can have OCD when it comes to any action that can be completed. It's a vicious cycle that consists of anxiety, compulsion, temporary relief, and obsession. If these excessive thoughts take up more than an hour of your day, then it may be time to see a specialist.

There are also other anxiety-related disorders like body dysmorphic disorder, hoarding disorder, selective mutism and illness anxiety disorder among many more.

5. Skin-picking and own-hair-pulling disorders (dermatillomania and trichotillomania)

These disorders are self-explanatory, they are impulse control disorders that make a person pick at their skin or pull their own hair. It can sometimes be associated with stress or present/past abuse.

6. Post Traumatic Stress Disorder 

PTSD is another anxiety disorder that can develop anytime after someone experiences a horrific event. The body is triggered in order to keep another episode from happening, and it usually results in someone being hyperalert most of the time. You can experience things like panic attacks, nightmares, emotional numbing, insomnia, and difficulty concentrating.

7. Attention Deficit Hyperactivity Disorder

Commonly known as ADHD, attention deficit hyperactivity disorder is diagnosed usually in children. Overall, it makes it hard for a child to sit still, concentrate, and could also impact learning abilities. It is possible that genetics can play a part, but premature birth, low birth weight, and other environmental factors can also cause ADHD. Usually one will experience difficulty sitting still, constant fidgeting, lack of volume control, no sense of danger, clumsiness, easily distracted, poor organizational skills, forgetfulness, issues with interrupting, inability to take turns, excessive talking and acting without thinking.

8. Anorexia Nervosa

When a person wants to weigh as little as possible, there is a chance they have this mental illness. They refuse to eat normally, and they do anything possible to reach the lowest weight that they can without dying.

9. Sleep Disorders

Insomnia, parasomnia, narcolepsy, and hypersomnolence are all sleep disorders.

Insomnia: This means you have difficulty getting to sleep or staying asleep for a long period of time. It can be caused by worry or stress.

Parasomnia: It's basically sleepwalking. You do things you do not remember and behave unusually. This runs in families and it may be genetic.

Narcolepsy: This has to do with irregular sleep patterns and suddenly falling asleep at random times. It can be genetic or caused by lack of melatonin among other hormonal changes.

Hypersomnolence: Excessive sleepiness that usually comes along with depression. It can be genetic or caused by drug and alcohol abuse, or maybe other sleep disorders.