grammar - Is it grammatically correct to use two past continuous tenses in a single sentence?

This question just suddenly somehow popped up in my mind.

Usually what I encountered in a sentence is in the pattern "past tense + past continuous"

E.g.:

I was doing homework when my mum came back.

I would like to know whether it is grammatically okay to use two past continuous tenses in one sentence?

E.g.:

I was laughing so hard when I was watching the video.