I wish I'd have a perfect answer for you , but I dont, sorry:)
That part of the game was introduced in the last update, (or 2 updates ago) thus, was never documented much.
I'll share the little knowledge I have about this topic!
Level of character is definatly involve somewhere.
My maincharacter , very rarely get minus days, or even normal days, its almost always +22 ( the amount of xtra quests, or lost ones, is also related to level).
(BTW, I usualy use that to know what I'll do with my main, , when he got only 202 quests, instead of questing I do mingle, to raise his favor, , then I'm good for another 12-15 days, before it happen again)
While with others questers I have way more often *normal* days.(I'm gonna start to take closer look on it, I'll make a table, I have charies or all levels between 30-40)
For my level 32 charies its roughly like that:
minus days (waking up late) : 156 (10%)
normal days: 164 (30%)
xtra quests (wake feeling like a million marks): 180 (60%)
Now, I'm sure, the WAY YOU LAST LOG OFF influence that alot.
(as it also have an impact about if you'll be sick or not in the morning, , or if your unoiled unblessed items will get hit by rust, and how bad)
(I dont know the exact numbers, percentage, but you can as me imagine the scale of chance to wake up late AND OR get diseased/hurt-rust upon awakening:
1 Sleeping in a suit = the lowest chance to have a tiny sniffle (get sick), the lowest chance to wake up late, as lowest chance to get hit by rust (minimal rust if it happen)
2 Rent a room
3 Sleep on tavern floor
4 Sleep by mound inn
5 Sleep outdoor with all camping gears (cooking stuff, tent, sleeping bag)
6 Sleep outdoor with part of camping gear (not sure if some items weight more than others, most likely, a tent shud help more than cooking stuff)
7 Sleep outdoor with no camping stuff at all. (With that way to log off, u can be certain to get hit by rust, if nothing is oiled nor blessed; u have the higest chance to have a tiny sniffle( be sick), loose guts AND loose quests.... (+ I think the loss of quest the next morning is worse that way)
(8) (I think it could be worst, as in being killed without fearies, loosing quests below 0, forcing u to log out, til next day, or so it was)
I think the best area is salamanders towenship inn suit! I highly suspect, mound inn, to increase chance of bad stuff to happen, , and I dont know about the inn by the dock.
Now I also know that fighters skills is part of waking up sick or not formula
... as in 3 fighters skills lower the odds to be sick, , and with 5 you are immune (not 100% sure here, but its roughly that).. So its possible that fighters skills also have a part in waking up late or not, , but thats a suspiscion.
I dont know why you've lost 40 quest, , if u are sure it was not because you ve been away over 15 days (loosing your clan quick ability).
May be last time youve quested you did log off outside a dc tavern? in the mounds or in the mountains?
Have you quit your clan ? (loosing Quick clan ability could lead to such loss of quest).
again, sorry,, I dont have a complete answer here, , few things are interwined here (your level, where you go to sleep, fighters skills, etc.) and waking up late or not, was in the last game update, thus the least documented dc update!
May you at least find here half answers, , or tracks to follow , from wich you can test and determine exacts odds of each possibles outcomes
I'm sure I could focus hard on it for some days with few dozens charies, to control all potential variables, and do various tries/errors, , and I could understand all this a bit more clearly, , but , , I dont really have time for this atm