Why does my diastolic pressure drop when sitting? But standing is normal?

It has to do with the water volume in your blood.

Water is the most important (and most abundant) resource in the body because every function depends on it - such as the muscles in your legs.

When you're inactive (such as sitting) the blood pressure is maintained at the default level it happens to be at the moment. When you stand up additional water is needed for this function (borrowed from other areas), which calls for an increase in pressure.

Because you are at rest...so diastolic should drop. When you stand up your heart has to push a little hearter to maintain blood to brain...therefore pressure goes up. Basic physiology

B/P goes up and down with every position of our body. Some one in pain would have 180/96 when they're in a recliner. But once they raise up and stand up, the numbers will change.

you need to ask your doctor this question unless you want to put it on healthtap and then a real doctor will send you an ernail back