VT/Maeve - it was after drinking much more tea/coffee than you describe that I'd get similar symptoms. It was more the throbbing heartbeat that you can hear that made me think of it. It was different to migraine symptoms - fortunately I've not had one of those for many years.
Just a thought - do you feel any better if you can get outside on a bright sunny winters day? I've found a bit of winter sunshine really lifts my spirits after lengthy periods where it doesn't seem to get light at all. If you can get outside in the bright weather it's even better.