I've noticed a tension headache over the last 3 weeks, that I wake up with, although in the last 8 days I haven't been home, and I haven't noticed the headache. I say "not noticed" because part of me thinks the headache is all in my head. But I do feel what I would describe as a "cloudy head" and a very dull headache.
I first thought it was a tension headache from clenching or grinding my teeth. I had never experienced headaches from this, but did, in the past, have an issue with clenching/grinding. Given that I've left my apartment and slept elsewhere for the last 8 days and didn't use my mouth guard (for clenching/grinding) and didn't complain of any headaches, this doesn't seem to be it.
I also thought it might be dehydration, but I drink a lot of water, and after spending time in a very dry state out west at high elevation, I was drinking tons of water and not waking up with a headache.
Doesn't appear to be a caffeine headache either, as I can go days without caffeine if need be.
I started to think it could be the air or an allergic reaction to something in my sheets or carpet. I am going to clean my duvet and its cover today, and probably vacuum my bedroom and the rest of my apartment. I have historically woken up with a little bit of decongestion, but nothing ever bothersome enough to take any drugs or anything. Usually water and some citrus or vitamin c in the morning for breakfast helps, along with a shower in the morning. But maybe it's possible this is related to sinuses.