Especially in the Whole Cake Island arc, we see Luffy recover quickly after eating/drinking and I remember in Impel Down, he did something that even looked like Life Return after recovering from Magellan's poison. Is it possible he is subconsciously using Life Return?
That's a good point!
Luffy also used conqueror haki for the first (few) time(s) subconsciously: shortly before the episode you describe, in Impel Down, to get rid of the wolves attacking Bon (chapter 536) and again shortly after, while trying to save Ace on the execution platform (chapter 569).
A while later, he also subconsciously uses goken to free boss Hyogoro and himself from the beheading necklace (chapter 946).
So that could very well be Life Return.