I wear the kind of contact lenses that you can sleep in, and I never get sleep in my eyes when I wake up. When I take my contacts out once every week and sleep, I wake up with quite a bit of sleep in my eyes. Why does this happen only without contacts?
If at first you don’t succeed, skydiving is not for you.
Just a WAG, but maybe your eyes become a bit irritated either when you remove the contacts or because the contacts normally provide a protective layer to the outside of the eye, and so more tears are produced when your eyes are nekked.
The same thing happens to me, but I imagine that’s because instead of the time-consuming and inconvenient method of noting how long I’ve had my contacts in (I have the disposable extended-wear type), I take them out only when one eye becomes so inflamed that I have trouble reading or driving.