hi dear nioted all your details your husband is on warfarin ,which is a blood thinner which prevent the formation of thrombus and clots of blood in heart in patient with atrial fibrillation atrial fib is a condition when every heart beat which orginated as pacemaker in heart can not produce a successful ventricular contraction a successful ventricular contraction is very important to maintain bl;ood pressure of the body passing out prob can also be because of other bp medications othostatic hypotension can be there ask you husband to change postures slowly use compression stalkings in legs doses of antihypertensive medicines are to be adjusted drink plenty water thank you