My dad he is 81. he sits up his bp drops to normal and sometimes to low and passes out 59/39 passed out . he lays down it rises as high as 190/90 at hospital yesterday but they never said nothing about it. any ideas why this could be happening?

At age "81", such variations in BP are common when changing positions, due to relative slowing of blood pumped by the heart due to the abrupt postural change. A BP of 190/90 is not uncommon in an octagenarian, and atherosclerotic blood vessel walls preventing normal flexibility can be record much higher systolic pressures. See a cardiologist for a correct assessment/possible treatment.