Performance anxiety, maybe? You want it that badly, you think about it too much, it doesn't happen. Maybe next time, try to relax. Slow down, do more hands on foreplay.
Your body just might need a little more TLC rather than wild hit the bed springs kind of body. I dont' know what you did before to get hot and heavy, but your body just might need more encouragement and less wild...if that's what you did.
Then again, you might need to see the doctor about this. it could be lack of blood flow to the area and maybe it should be "looked at" by a doctor. Embarrassing, maybe, but if you need to, that's what they are there for....I believe it's a urologist specializes in the male 'body part', or you can see your primary care if you have one. Heck, it's worth it if it means getting your sex life back to where you want it to be and no extra foreplay is working for you.
I also do tend to agree with what other people are saying. To eliminate any possible social crap such as drugs and alcohol including cigarettes, if you still are having troubles, then see your doctor.