Ever noticed that the Imac is a single piece of plastic around most of it? If you look closely, you will find that all of the venting for excess heat are on the bottom of the case.
If you ever have problem with your Imac, and you think the problem is heat related, rotate the case so that the vent holes are on top. That way, the heat can rise out of the case and you can continue working on your Imac.
Keep a copy of this message close at hand or search the Apple Web site for Imac Troubleshooting, by using the keyword, Hot Apple Turnover.