There are rules for sleeping on WSG 65 but they are too simulationist.¹⁾

Instead, apply the following rules:^Ex

Sleep required is as follows:

Failing to get the needed sleep applies a cumulative -1 to all to-hit rolls, AC, and saving throws for each night past that 1st night, up to a maximum of -6 (following the 7th consecutive night of insufficient sleep).

Any character wearing armor to sleep more than 1 night in a row takes the same -1 cumulative penalty mentioned above. It will stack with the “sleeping in armor for more than 1 night in a row rule”.

A single night of proper sleep reduces the standing penalty by 3.

For example, sleeping in metal armor 2 nights in a row (-1 penalty) and only sleeping 8 hours each night (two -1 penalties) means a -3 penalty until a proper night of sleep is achieved.

Of course, though the penalty caps at -6, the DM should rule that a character simply cannot adventure if they go for a long time without proper sleep.