Sat on leg for 2hrs, stood up entire leg numb w foot very swollen red, relieved in 15 minutes now centralzed back pain 1hr. blood clot? was active today

Doubt blood clot: Unless you were almost motionless for those 2 hours (and even then), without knowing if you have any other risk factors (smoking, etc), i'd say it's extremely unlikely that you'd develop a clot that quickly. You were probably sitting in a position compressing some blood vessels and nerves somewhere and getting up eventually relieved that. Back pain also probably from how you were sitting.