Somebody help me figure out what's wrong with me?

I've been experiencing incredibly flippant moods for the past day and a half, that is, after coming back home. Literally one minute I'll be really manic and I think about how successful I could be in the future and I make these plans and the potential power feels so good, and then the next minute I'll be helplessly lost in an abyss of 'there's no purpose, there's no meaning to life that's worth living for, killing myself would be such a relief.' I know for a fact that I don't have any serious mental illnesses albeit this does sound serious. Is this normal after a very traumatic period in your life? Will it pass? I feel like just working on my life despite the agony that I feel when I get like this so that I will ultimately be successful and I can start to be happy from then on... help?