On FF I think it means you didn't sleep well, as when you have a restless night your temperature is often different (I think someone said lower, but really don't quote me on that) than it would have been if you slept well.
thanks guys i slept really well last night so good job i didnt tick it today i do get times when i have to go to the loo like 3 times a night should i tick it then? cause i am then loosing sleep