1. Rain. I'm serious.
2. Mosquitos. Hence, powder baths & insect-repellent
application before sleeping.
3. The cold. You'll experience it even in Singapore, when out in
the field. It usually hits at about 4 or 4:30 in the morning, when
daily temperatures reach the lowest. You'll usually wake up needing
to piss as well, given how your body's self-heating process creates
a full bladder.
3. Scorpions. Snakes aren't a big problem, maybe in Brunei but then
you're taught to spread sulpher around your sleeping-area
circumference prior. But many soldiers like to remove boots &
let their feet "breathe" at night when sleeping, & in turn
scorpions like to climb into the footwear due to the warmth inside.
Bites can & do occur locally, when disoriented or sleepy guys
forget the checking drill when waking up for stand-to or
night-guard, etc.