1. What is the link?
Depression

2. What is the link?
Bipolar

3. Signs of Depression
Depression can occur in people of any age, gender, background and ethinicity, however it is more common in women.
In order to be diagnosed with depression you must have at least 5 out of the list of symptoms presented by the DSM:
Constant feelings of sadness or anxiety
Constant Low energy, feeling tired or fatigued 
Under- or over-sleeping, or waking frequently during the night 
Poor concentration, thinking slowed down
Loss of interest in things that were once enjoyed e.g hobbies or seeing friends
Low self-esteem and feelings of guilt
Loss of interest in living, thinking about death, suicidal thoughts
Loss or increase in appetite
These symptoms must be present for a minimum of 2 weeks and must not be due to a bereavement or loss of some sort

4. Signs of Bipolar
Bipolar disorder involves both depressive periods and their opposite, which are known as elations or manic periods. Symptoms of the depressed phase are the same as those of depressions, however the elations can be:
Feeling elated, enthusiastic, excited, angry
Increased energy, over-talkative or over-active
Reduced need for sleep and difficulty in getting off to sleep
Racing thoughts, 'pressure in the head', indecision, jumping from one topic to another, poor concentration
Increased interest in pleasurable activities, new adventures, sex, alcohol, street drugs, religion, music or art
Excessive and unrealistic belief in one's ability
Thinking that one can live forever, taking reckless physical risks
When suffering from these disorders there are ways the individual can try to help themselves with things such as regular exercise and reduction of caffeine and alcohol, however ,these will not alleviate the symptoms completely so there are other treatments such as medication and various therapies