What Causes Numbness In Penis?

I am a 22 year old male. Sometimes when I am sitting down or leaning against a surface my penis seems to go numb equivalent to an arm or leg falling asleep due to no blood flow. I don't even notice it till I sit up and immediately feeling comes back (like pins and needles). 5'10 and 220 pounds. My penile health has been fine. What should I do to make this stop happening? Is this even serious?