Yes most of the web and UK public are going on about this and that noise that sounds like pong, but what the hell does happen if the timer runs out?

I never saw anything of the first season of Lost, I was always out or focused on something else, but you could not escape from the buzz and hype. Last night the first two episodes of season two were aired on Channel 4, but in the build up they have been re-showing the first season during the day, to which I caught enough to understand the basics.
However I’m not sure who ‘the others’ are and why every one was so scared about going to sleep or rather making through till the morning. But those facts are tiny in comparison to the burning question, what happens if the timer runs out?
In the end I watched the third show which was show on E4 straight after, still no answers but it does seam a bit strange. Does human nature prevent you from walking away? Is it the ringing phone syndrome, where you just have to answer it?