I have a tingling/numbness in my scalp - just on the top of my head - for about 9 hours now. It's happened before several times. It's not painful.

Need some testing. You may either have a painless variant of ALLODYNIA which is typically associated with migraine types of headaches as an aura or premonitory marker and believed to be the propagator if not the consolidator for the long lengths of some episodes of migraine. Or there could be metabolic or other structural items causing symptoms for which labs or testing need to be done. www.healthtap.com/drsaghafi.