Mid-squat a while back I fucked something up in the very top part of my spine, about where my neck starts. From then on, whenever I would train, about halfway through a set this powerful pressure would build up in that area and it was very painful and completely ruined my workouts.
A good friend of mine is a chiro, so I saw him immediately. He said it could be a pinched nerve. He did his routine on me and told me to go train and see if it was better. I'd say it was maybe 20-30% better, but only temporarily.
I did what I didn't want to do and took it really easy on the weights, taking long rest periods in between training days and not doing heavy compound movements, only isolation shit that caused no pain.
About a month later I think it was gone and never returned. Not sure if it was a pinched nerve, but I thought I'd chime in with that.