So I'm 36 weeks and I'll be 37 on Wednesday, but tonight, after I showered, all of a sudden I became…

So I'm 36 weeks and I'll be 37 on Wednesday, but tonight, after I showered, all of a sudden I became extremely exhausted and could fall asleep anywhere I was laying. I also felt out of breath and felt my heart racing. What can that mean? It's happened in intervals a few times now but there's no pain, it's just very exhausting waves..