Learn Russian: Раньше он всегда просыпался поздно.

In the past tense, reflexive verbs use -ся after consonants and -сь after vowels. Since the masculine past tense ends in the consonant -л, we add -ся. If the subject were a woman, the verb would be просыпалась (ending in the vowel -а, so we add -сь).

Does the -ся at the end of просыпался mean he was waking himself up?

Essentially, yes! The ending -ся is a shortened form of 'self'. In English, we just say 'woke up', but in Russian, verbs that describe an action happening to the subject without involving anyone else often require this reflexive ending.

The word раньше comes from рано (early). Why does it translate to 'in the past' here?

Раньше literally means 'earlier'. In Russian, using 'earlier' is the standard, everyday way to express 'previously', 'used to', or 'in the past'.

Is the letter д in поздно pronounced?

No, it is silent. When Russian has a heavy cluster of consonants like -здн-, the middle letter is often dropped in speech to make the word easier to say. You pronounce it as if it were spelled позно.