I work in a call centre & for the past few weeks,every time I get up & start walking I get a pounding in my head & feel lightheaded,i have to stop till it passes which is normally not long,it only happens when I start walking after ive been sitting,i also suffer with anxiety & don't sleep very well either but this is worrying me cos im goin on holiday on 17th & worried bout pressue on my head when flying,what could be causing this?