Hi, thanks for writing to HCM.
It seems that you might have sustained a soft tissue hematoma
could be due to the pressure effect of hematoma over the superficial cutaneous nerves or due to a direct trauma during fall causing neuropraxia.
Generally these issues will resolve spontaneously with 4-6 weeks. In Diabetic patients there is a possibility of the hematoma getting infected (so beware if you are a diabetic).
There is no harm in using the heating pad
Hope this helps