People who are natural "larks" will not be larking about this weekend, a sleep expert warns.
Later daylight will disturb larks the most
They will be hardest hit by the clocks being put forward, when the country switches to British Summer Time.
But Dr Adrian Williams, of Guy's and St Thomas' NHS Foundation Trust, says larks will suffer most because they are more sensitive to the light.
He said there was little people could do about whether they were larks or owls as it was down to their genes.
Dr Williams said environmental factors such as light and noise obviously contribute to our ability to sleep at any particular time of day.
But research carried out by his team in 2003 found that whether someone is a lark or an owl, when they want to sleep and when they are at their most alert is also determined by their genes.
So there is little people can do to change whether they are good earlier or later in the day.
Dr Williams, who runs the sleep centre at Guy's and St Thomas', said: "We are generally a sleep-deprived society and most people sleep, on average, for an extra two hours over the weekend to make up for the sleep they have missed during the week.
"Clearly losing an hour of this extra sleep might lead some people to feel a little more tired than usual, particularly in the afternoon when people naturally feel a bit sleepy, so it may be wise to plan a restful Sunday this weekend."
Jessica Alexander, of the Sleep Council, said: "There is some evidence to suggest that insurance claims go up twice a year when the clocks change.
"It does have an effect on people's sleep patterns."
And she said that, because being a lark or an owl was "pre-programmed", there was not a lot people could do to change it.
"It would be interesting if employers took our general tendencies to 'larkishness' or 'owlishness' into account in terms of productivity."
She added that those who felt they were larks should take that into account this weekend.
"They should take it easy this Sunday and Monday and not do anything that takes great concentration."