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Over half of all over 65 year olds have problems sleeping. In our final Sleep Watch film, Michael Mosley met Beth - she regularly finds herself waking up at about 1-2 in the morning and can't get back to sleep.

Michael and Beth went to see Professor Dijk at the .

Prof Dijjk explains that we have more deep sleep when we are young and this deep sleep declines rather dramatically as we get older. By the age of 75 many people are getting none of this restorative deep sleep at all.

The results of the test that Beth took indicated that she is alert. Despite this lack of sleep, she's not extremely sleepy. This is something that mirrors Prof Dijk's research - that healthy older people are very alert during the day and in fact they are less sleepy than the younger individuals,

Although Beth may be getting less sleep than when she was younger, in fact people her age don't need as much, which may be why she keeps waking up in the middle of the night.

The problem seems to be not that Beth is not getting enough sleep, but that she is in bed for too long. When you're in your 60s or 70s trying to get eight hours of sleep maybe not be the wise thing to do as you may only need seven.

To check whether lack of sleep is affecting your alertness take the .

A normal score is less than 7, 8-14 is mild daytime sleepiness, whilst 14-20 is moderate to severe and 21 is the maximum. If you have a level of 20/21 it is very dangerous to drive.

Click here to see all of the One Show Sleep Watch films.