what is the cause of very painfull foot at the heel like throbing pain increases while am sitting down?

Answer 1

Maybe you have arthritis. Have your uric acid level checked.

Answer 2

I am not a doctor, but, it sounds like you may have Plantar Fasciitis it is when the muscle that connects from under your toes, to your heel, gets damaged, sometimes torn. It hurts more when you are sitting down, and really bad first thing in the morning.
If you do some stretches, like pulling your toes with your fingers, to stretch that muscle, and rolling your foot over a frozen water bottle.... standing on some stairs (going up).. with your toes on the stairs, let your heels hang off to stretch.
The most important thing is to have your foot stretched for several minutes before you get up... EVERY Time, from bed, or from chair, or anywhere you are sitting.
It will eventually get better, but it takes a LONG time.

Answer 3

Consider a heel spur or plantar fasciitis. See an orthopedist.

Answer 4

It could be due to poor circulation of blood in your lower limbs.See a doctor immediately.