I woke up this morning to a bad smell in the upstairs of my split-entry house. It smelled like burned hair. It does not smell downstairs where the electric heat pump and hot water heater are. It is not a smell from outside. I checked the stove, oven, hair dryers, appliances, etc. and cannot find an area where the smell appears to be stronger. My house is pretty small and it has permeated the upstairs in about the last 2 hours. I turned the heat off, but that hasn't done anything.

Any idea what this might be, or what else I should investigate?

Thanks