4am wake-up

At 4am this morning, I was awoken by my husband screaming. Though I was quite startled, I right away realized he was screaming in his sleep. I turned over and nudged him (Is that the right thing to do? I don't know.) and asked if he was alright. Apparently he had some nightmare involving ghosts, but he was fine. I've been in the same room with sleepwalkers, sleep talkers, and snorers, but this is the first time I've experienced sleep-screaming. It's a bit scary, and I hope it does not happen often. I'm a pretty deep sleeper myself (I did not wake up when my husband accidentally elbowed me the other night though it woke him up), but a scream or shout seems to do it.