Foot pain, odd spot.?

I got this random foot pain well cramp yesterday it was right where my arch and heel meet on the instep of my foot. What would cause that kind of pain?
I'd not just been walking or anything, I was sitting on the couch with my feet up and it just started.Foot pain, odd spot.?
There is a tendon that runs from your heel to your toes, and which that form the arch of your foot. Pain in this tendon is called plantar fasciitis. When you sit a long period of time the tendon contracts. The muscles in your calf join the tendons in your foot. When you sit with your legs out straight, the tendons in the calf pull on the heel are also stretched, which pulls on the tendons in your foot. Cramps occur because the muscle tissues become temporarily depleted of magnesium from being over-stretched, which causes the muscles to cramp. Muscles cannot relax without magnesium. This can be prevented by taking a magnesium supplement, staying hydrated, and stretching. If inflammation develops, it's much harder to get rid of the pain.
That is strange, my mom has achilles tendon pain because she referees basketball, and because of any pressure, even if it was 2 days ago, it will hurt. Maybe it's from putting pressure on it a while ago. Hope that helps.
It's called plantar fascitis and it is very painful. See a podiarist.