what is this symptom called?

ok i guess its kinda like a head rush, but for me it has happened right before I get sick, i think its stomach bug symptoms. I will be calm usually when it happens. The other day it happened when I was laying in bed, I had a space heater turned on so I was sweating when I woke up very early and had this slightly nausea's feeling in my stomach and all of a sudden, I feel a bunch of fluid rush to my head and I get really anxious feeling and nausea. half the time when this happens I end up in the hospital from continous vommiting, but this time I turned off my heater and layed down and tried to calm myself down and it went away. It seems like it could have something to do with temperature, it happened most often when I was deployed in Iraq, and then it started happening again when I got a job working a dairy department at a grocery store, walking in and out of the cooler and staying in there for a couple hours at a time.

by the way im sure these symptoms are probably related to my mercury poisoning I am just very curious what this weird head rush is and whats causing it. any suggestions?