What Causes Strange Sensation In Head?

recently having strange episodes concerning my head, they ve been happening more often and 15 or so at a time. its like a wave starting from the top of my head, like a garage door closing. i feel nauseous, then my vision wavers, it passes, then happens again. i feel like i have to hold on, then it passes and happens again. just lost my insurance after 25 years last month.