confusion in interrup handler

Hi All, Pls help me here to understand the following scenario: As we know, we cant sleep inside interrupt handler. But what is the reason for it? If I put sleep inside the handler code handler, handler code will not complete and none of the process on that particular processor will ever will execute. So it will be kind of deadlock. But what if the system is having multiple processors ? Is it safe here to sleep ? If not what is the reason ? Best regrads, Krishna