Last Friday When I Was Driving (fairly Exhausted After A

Last Friday when I was driving (fairly exhausted after a bad night's sleep), I suddenly felt very faint and dizzy whilst coming off the motorway. I nearly pulled over, but there was nowhere to stop and then I felt it pass and I was ok. I put it down to being tired, but today whilst sitting still and talking on the phone, I had another attack and it felt like the world was spinning left to right. I have had BPPV twice in the past and it's not the same - this isn't due to any particular positioning of my head. I still feel mildly nauseous and a bit weak. This is possibly due to being anxious about it. I'm not tired (I don't think!) so why is this happening?