Bipolar mood swings last for longer periods of time (at least more than 4 days for each mood, although it's usually much longer than that..in some cases many months). Mania is the "good" mood, but can feel terrible for a lot of people in that they are moving faster than their bodies and in some severe cases, experience psychosis (bipolar 1). I know a good bit about it because I was originally diagnosed with rapid cycling bipolar type 2 before my BPD diagnosis. It's unclear if I do still have underlying bipolar, but it's been stabilized by my mood stabilizer anyway so my psychiatrists aren't too concerned about it since lamictal is also said to relieve mood swings in BPD as well. BPD is certainly the main issue for me.