We can assume Sandman is doing a pretty good job usually at least, if that qualifies as a nigthmare for Ashley. Ruined breakfasts are pretty annoying though.
2nd panel: startet -> started
Never trust your dreams to a sandman who can’t spell.
Ah, but the real nightmare is when the /last/ of your cereal and the /last/ of your milk go in the bowl — and then you discover that the milk has gone sour (because somebody left the fridge open overnight).
Another classic is pouring the last bit of milk from one milk carton over your cereal thinking there is another full one, only there is none. So you’re left with slightly soggy but mostly dry cereal.