I hate this feeling of being in a fog when it happens. I know for me there can be all sorts of reasons for it. I have to look at meds, eating and sleeping patterns, need to increase exercise, and need to look at what's causing stress to reduce it which influences this foggy feeling. Changing these things can help reduce it, and help with clarity.

A friend who had this feeling went into to the doc as nothing seemed to help and it turned out there were medical issues going on. If these things are not helping and have not had a physical lately, as you described pain (physical pain?) associated with it too, it might be beneficial to see your doc to get checked. If emotional pain, it would be worth talking to someone, T or counselor at school to get some insight and help. It's not worth having to deal with alone and letting things slide or snowball.

I hope it resides soon. Hang in there!