Bulgaria switched to winter time this morning. At 04:00 the clocks went back one hour, to 03:00.

On Wednesday the Bulgarian Institute of Metrology reminded people to change their clocks on Sunday, 25 October.

How it all started: Clocks go back one hour on Sunday, 25 October

The body needs time to adjust, sleep medicine specialist Dr Petar Chipev told BNT. He said our internal clock is still running on the previous day's time. Anyone who used the extra hour may have noticed this morning that they slept a little longer.

"Still, such changes take anywhere from a few days to a week, depending on the state of the body," he said on the programme "The Day Begins".

How fast a person adjusts also depends on their daily routine and lifestyle, the specialist said.