I'll admit that I'm not an expert on which songs were used when, but I'm pretty sure 'Comfortably Numb' was never used on the show... link lists all the songs used on the show and 'Comfortably Numb' doesn't appear anywhere.
Can you describe the scene you are thinking of? Maybe we can identify the song and the episode if you can tell us a little more.

The song seem so appropriate to House's situation and his addiction to pain medication. I thought it had been used during a scene of him in agony or spaced out on Vicodin

I can't be sure that the song was ever used in any episode.

I don't think it ever was, but you're right, it is a perfect song for the show. Shame they never used it but they did use a lot of good songs overall.