It means we went to bed mad, slept for a while, and then woke up.
It’s OK to Go to Bed Mad
L. Mattingly
141

One of the things I deeply admired about the relationship my wife and I had was even that though we had ordinary arguments and went to bed mad, somehow in the first hour of us both laying there still amped up, one of us would find the hand of the other and we would hold hands till we fell asleep. From that moment onwards we both knew whatever it was was workable and inconsequential in the grand scheme. Many mornings we would wake up in the same position. The next day there would be no grudges and no lingering issues; it was always a good day. Do everything with the thought of what is best for “Us”. The tit-for-tat games are a death sentence on a relationship.