Randomly engorged 8 months pp?

My daughter has been EBF since birth. She has been sleeping 12.5 hours a night for nearly 3 months now. My supply adjusted to the change and we have had zero issues. I pump once a day before bed for about 20 minutes and get 4-5oz.

Last night I got a little on the lower end of my usual amount, but it was normal. At 5:00, I woke up with crazy engorgement. My breasts were very full and super lumpy. It has subsided now, but I am freaked out. What would cause this?