Feel tired on Mondays? Don't lie in at weekends Dr Gregory Carter, a specialist in sleep medicine at the University of Texas Southwestern, said: "A great myth of sleep deprivation is that if we miss sleep over the course of the work week, we need to catch up on an hour-by-hour basis at the weekend." The body can accommodate a delay to the circadian clock of up to an hour, meaning that a short lie-in at weekends is unlikely to have any significant effect on tiredness on a Monday morning. However, delays of up to two hours or more can throw the body out of sync, making it more difficult to get to sleep on a Sunday night and even harder to get out of bed the following morning. Any "sleep debt" built up by going to bed too late during the week can be balanced out on Saturday or Sunday simply by getting eight hours of sleep, because the brain rests more efficiently when someone is tired, said Dr Carter. The most effective approach is to go to bed earlier rather than sleeping later at the weekend, in order to continue waking up at the normal time while getting the optimum amount of rest. The approach is beneficial even to insomniacs. In contrast, staying up late on Friday or Saturday nights and having a lie-in the following morning - especially when coupled with other behaviour which harms sleep quality such as drinking alcohol or checking emails just before bed time - makes Monday morning all the more painful. Researchers have previously shown that even hitting the alarm's snooze button to get a few more minutes" rest after a sleepless night can make people feel worse than simply getting out of bed.