Researchers in a sleep laboratory woke people up and asked them to perform some random arithmetic (addition) tests. One minute after being awakened, the subjects’ scores were just 65 per cent of their best; their optimal scores were seen 20 minutes after getting up.
These amazing findings are bad news for people who often have to undertake difficult tasks almost immediately upon waking, including firemen, soldiers and – er – doctors (JAMA, 2006; 295: 163-4).