One problem with sleep right now is that if you get woken up in the middle of the night it can be very, very hard to get back to sleep. I don’t know exactly how it currently works, but it seems to be that in order to fall asleep you need to exceed a certain threshold of tiredness. The problem is that this is done very numerically, so if you go to sleep when you are just past that threshold, and sleep for two hours before being woken up by cold/asthma attack/noise/whatever, your tiredness will decrease past the point where you can easily fall asleep. You kind of end up trying to sleep and failing until your tiredness exceeds the threshold again. (or you take a sleeping aid of some kind). This can make asthma a huge pain in the ass, and it can be even worse than insomnia because at least with insomnia once you get to sleep (with sleeping aids) you stay asleep. Asthma can wake you up every hour and require a sleeping pill to get back to sleep each time.
(Someone can correct me if my depiction of how sleep works in the game is wrong)
This isn’t really how sleep works. When you get woken up from sleep your body takes time to return to an alert state. That can certainly be accelerated by adrenaline if the thing that woke you was worthy of adrenaline, but if you just wake up shivering, your brain is still very much in a slumber state, and it can be very easy to get back to sleep as long as the thing that woke you ceases.
The simplest way to fix this would be to apply a ‘Drowsy’ modifier upon falling asleep. This modifier lasts for a brief time after waking (say 30 cycles). While drowsy you can return to sleep much more easily than you would at your current tiredness. In the event that you are attacked or see an enemy, the modifier will immediately end as adrenaline rapidly erases the drowsiness.
For the sake of flavor, while drowsy you also perform tasks more slowly. Since everyone knows what it’s like to wake up in the morning sluggishly make coffee. Speaking of coffee, caffeine would speed up the recovery from drowsiness.