Scientists at Auckland University say they have discovered why general anaesthetic leaves many patients with the sensation of being jetlagged.
They say the drug freezes the body clock, and have quantified their findings by studying bees.
Researchers gave the bees a common general anaesthetic to see if it would disrupt their extremely accurate sense of time.
By tracking the bees' flight paths and behaviour after waking up, the researchers could work out what time of day the bees thought it was.
They found that six hours of anaesthesia would disrupt the bees' body clocks by four to five hours.
The scientists now want to investigate whether jetlag can be reduced by treating patients with light.
They say doing so could improve patients' recovery and the healing of wounds.