I noticed a few hours ago a lump behind my right ear. is it safe to sleep tonight or should i visit the hospital?

Probably not urgent: A lump behind the ear may just be an enlarged lymph node that could appear when you have some kind of viral infection such as a cold, if if you have a scratch in your scalp. If it is not painful, red and spreading and you don't have any other symptoms, feel well as usual, then you can sleep tonight and make an appointment to see a doctor tomorrow. I see this all the time with kids.

Probably safe: Paul, the lump behind your ear is probably a lymph node. They usually swell in response to infection, but can also swell for many other reasons. If it is red, tender, painful, or you have a fever, you should probably be seen as soon as possible. Otherwise, it can most likely wait until morning. Hope this helps!