Yes it's annoying, but the fact is that a lie-in is more likely to make you feel groggy than better.
As we all know, the human body is an amazing thing - our natural body clock prepares the body for waking an hour beforehand by making sure that the right hormones are flowing, so you can hop out of bed at the appointed hour. Amazing.
But the body can only prepare if it knows when you're going to get up. So if you mess it about getting up at 6.30am on a weekday and then 9.30am on a Saturday morning, your body has to readjust constantly - which can make you feel groggy.
Top tip for a great night's sleep and avoiding grogginess on waking: Try to stick to a regular sleeping pattern and don't lie in at the weekend - it will help you synchronise with your body's natural rhythms.