i think the word "stressed" was wisely used to describe what you're going through. i know for me when i'm stressed my bipolar is the first thing that will pop up. as a result i have to attempt to reduce stressors in my life to create as much balance as i can.
i too think exercise is very useful to reduce stress and avoid the depressive mood swings. putting yourself on a daily regimine to meet your goals...exams...will help to eliminate some of the exam stress.also.
not sure if i can make out what you mean about your friend but one thing that helps me in difficuolt situations is that i do not have control over other people's behaviors towards me. if i keep the focus on myself and how i conduct my own affairs the rest seems to work out all by itself...
..and time is a great healer.
i wish you well on your exams. just focus on a study routine and you'll get done what needs to be done...and chatting about all this will help you too.