Hi
Welcome to the MedHelp forum!
A heat sensation or sudden feeling of warmth can be a sign of blood clot or deep vein thrombosis. It can also be due to pinched nerve or due to diabetic neuropathy. For diagnosis first a duplex ultrasound or color dopplar would need to be done. If this is negative then a nerve conduction study and test for diabetes. If there is a chance then if everything else is negative, then lupus may need to be tested for.
So consult your PCP, a vascular specialist and a neurologist in that order.
Take care!
just see your GP mate he/she will refer you to whoever you need to see thats what they are there for