Answer
Well, since you wouldnt normally have it I think it is from the not showering. It probably made your scalp really oily so the skin is all built up as dandruff. It happens to me on occasion, and I just continue as normal and it goes away after a few washes. Try to use enough shampoo when you wash your hair to clean the dandruff off of the scalp, but not so much that it makes it dry (because dry scalp can also cause dandruff!) Scrub it well until if feels as though it should all be gone. If its still there in abundance after maybe two washes, you might consider buying something special for it. But you probably wont need to, I never do.