Have several ideas, just do not want to cause any confusion to you, one, is possibilty, Bipolar disorder (I have Bipolar-II mild) what you described are some of the thousand different behavioural traits, more info can be found at this website on the "under disorders", and loads of info in books I put under suggested reading, in the Bipolar forum.
Other causes can come from substance abuse, hormonal imbalances, including thyroid (especially women), "good old" stress, Borderline Personality Disorder, just to name a few.
The best thing is to go for a physical and then follow with a mental health professional or vice versa, there are too many causes that can be attached to your described behaviour/symptoms. I would look into a mental health professional if I were dealing with what you described, and get to the source, reducing the stress of not knowing.
I DO have many ideas, but sometimes a person doesn't want to accept they may have a mental disorder, once one finally decides to accept there is a possiblity of one or several, then treatment can follow, and there are many helpful treatments, some may just be talk therapy and an attitude adjustment in adjunct.
I wish you luck with this and hope you seek help, you can always feel free to come here and chat with others at our various forums, or even check and see if anyone is on "chat", usually in the evening hours is when most visit "chat".
We can offer support but are not qualified to give out diagnosis, nor would anyone want to take the responsibilty in misguiding others, it is always best to get a professional opinion.
Take care,
DE

In giving advice seek to help, not please your friend
SOLON