I can definetaly relate, 1 minutes your on top of world and 2 minutes later your planning your own death. In the past I've kept reapeatly switching for days. I was told the short ones that change quickly and violently are to with my 'BPD'. Whatever the cause though there very very upsetting and distressing.
What about in the in between moments having a bath or doing a actititvy that happens you personally relax, even if it doesn't help to prevent the mood swings and lessen them, it might help you stop thinking and worrying about the next one even if only a little bit just to give a small break.
I would defentialy suggest talking to your doctor about your meds if you feel thier not working. Sorry I can't help more but your not the only who has had these sort of experiances. Hang in there and I hope things get better very soon.
*hugs*
Frankiex