Debí dormirme andando

[Wahooka]

Here is another phrase from Tintin comic book.

CONTEXT: The Captain has hit a tree and passed out and then awakens.

PHRASE: Debi dormirme andando.

[AngelicaDeAlquezar]

"Debí" is introducing the hypothesis about why he's just waking up when the last thing he remembers was to have been walking.

[Kalinin]

Although I'd prefer to say "Debí haberme dormido andando"

[Julvenzor]

Cabe destacar que puede distinguirse entre "deber" y "deber de". Aunque se admiten ambas formas para hipótesis, con la preposición se anula cualquier ambigüedad:

Debí de haberme dormido andando.

Un saludo cordial.

[Wahooka]

Okay, thanks, still a bit confused, I'll work on it.

If you can translate into an English sentence, that might be easier for me,
but maybe there is no literal translation.

[AngelicaDeAlquezar]

There is a close translation. Try a sentence starting by "I must have..."