Here's my follow-up after my visit to the GP. He told me to get X-rays done of my head and neck to check for sinus and spondylosis. I got them done and it seems that there's no problem with my sinus....
I have almost the exact symptoms as you. It started one night around 2 weeks ago when I tried to fall asleep. It was very late (around 2 am) and I was feeling this pressure at the back of my head...