Macbook goes into hibernation when uploading to youtube

I have 10 videos queued up for upload to youtube

But I'm havinng trouble - my Macbook goes to sleep

What's the best way of stopping sleeping?

OK... without looking, I'm sure there will be a power setting that I can switch on settings in OSX that keeps the laptop awake always...

But... I do want it to it to go to sleep - when it isnt doing anything - i.e. has finished uploading

What's the best solution?

Thanks

Omar