Apologies for the name change but I could do with some none biased advice. DP has suffered mood swings since his early 20s but IMO seems to be getting more more severe. Latest example is 3 days ago he was so hyper it was ridiculous, we went to visit his parents and he was just acting like a 3 year old all day, constant laughing, huge smiles, high spirits, loved everyone, loved life, he seemed so happy and excited about anything and everything. Yesterday morning he dragged himself out of bed, made a coffee and curled up on the sofa at 8am. I asked if he was going to get ready for university and he said he didn't want to go. I asked why and he said he just couldn't face it. He hated it. He wasn't even sure he was doing to right course anymore as he didn't like doing the job he was training for 
, he started slagging off his fellow students and going on about how he hated them all and that he couldn't deal with them. He then started going on about the past and how certain weather reminded him of depressing times and how sometimes he just wants to get on a plane and never come back. He went to uni, came home and went to bed.
This morning he got up, coffee, cereal, set off early to uni and came back telling me how much he loved the course and couldn't wait to qualify and we're going to do all this cool stuff and he can't wait and he loves me so much etc etc.
He's always like this. When he's down he's horrible to be around. He snaps at me and I can tell he often can't stand being near me. I almost see him cringe when I speak. He doesn't want to get up, he doesn't want to do anything.
When he's high he's amazing and can't do enough for me and manages to excite ME about our future.
He won't seek help as he's frightened the university will find out and deem him unfit to work. I worry though because when he's high he does really odd things and that is getting worse too and it's only time before he does something at uni and people start to wonder.
How can you help someone that refuses to admit there is a problem? and could this be general mood swings as opposed to bipolar?