I'll always remember what my BMT PC 2WO Tum Tuck Seng told me...
Don't stand when you can sit, don't sit when you lie down, don't just lie down when you can sleep. 
Shall always remember sweating like mad under the sun, with sandflies and what not flying all over us, yet we just lay there and slept... Cadet training... >.<
But of course, i would prefer taking a nice long, hot bath before crawling under my covers...