Like, out of nowhere, you play better than you've ever played before.
The first time this happened me was on 6-6-06, and my nametag was 666 (lol), and I raped with Roy, playing twice as good as I've ever played as him.
Not too special, but 2 days ago, as Mewtwo, on the cpu's last stock, I did this combo without even thinking about it, my fingers just moved. I went for a uair, and wanted to follow up with a nair, but instead I fflc'd it and did a usmash. I went for another uair, then wanted to do a djc'd fair, but I did the same thing as before. I wanted to do another uair, but somehow I did a backwards full jump with a perfectly timed dair, sending them diagonally into the pit. I'd think it to be a coincidence, had it not been for that part, I felt my fingers move on their own. And the weird thing is, it was a perfect combo, the cpu had no time to react(though I highly doubt this would work on DI'ng opponents)