Happens to me all the time. I was afraid for a while that I was developing dementia, but I've now had two pdocs tell me it's a combination of meds and the brain damage that results from having repeated severe bipolar episodes. I'm glad I don't have Alzheimer's, but I can't fix the bipolar and I can't stop taking medication. So I just put up with it, and try to laugh about it because it's going to keep happening.