WHAT’S THE DIFFERENCE BETWEEN... NAPS

■ The power nap (10-20 minutes) Energy boost, easy to wake up from. Best for getting straight back to work.

■ The ideal nap (26 minutes) Improves alertness and problem solving – as proved by NASA.

■ The bad nap (30 minutes) Causes “sleep inertia” – a similar feeling to a hangover which can last up to 30 minutes. Best to avoid.

■ The memory nap (60 minutes) Improves shortterm memory. Some grogginess. Best before a presentation or important meeting.

■ Full sleep cycle (90 minutes) Improves creativity, emotional memory, dreams.