I don't believe David ever did.
Here is a link about it:
http://en.wikipedia.org/wiki/Biofeedback
It was the subject in an episode of the TV series
In Search Of

Did David ever try biofeedback? It did nothing for me, but that doesn't mean it can't benefit others.
Many years ago my doctor referred me to his friend for biofeedback. I really tried to make it work, but all it did was make me fall asleep. It was a total waste of time and money. The woman who did the biofeedback was an absolute moron. She desperately tried to convince me that I really needed her very marginal services. I thought that was unethical. She must have been desperate for business. I never saw any other clients there. I told her I would give her a call if I ever had trouble getting to sleep.

OK Thanks!

David tried different potential cures(as seen in 'Rainbow's End' for instance) but they never worked, and it should be remembered that the Hulk could emerge in David's sleep, or under hypnosis(as seen in 'Married') so it was a complex internal dilemma that afflicted David. He even tried becoming a hermit to avoid people(hence conflict) in 'A Solitary Place', but that didn't last either!