I’ve been rewatching In Space with Markiplier (basically on and off since Iron Lung came out) for Fanfiction research. Because I’m insane. As one does. Like I’m back in college.
And I’ve watched the intro video at least 200 times at this point (since its initial release)…And I somehow still keep figuring out new things each time (tidbits or soundbits).
And I’m sure this isn’t SUPER new or revolutionary. But the intro ends on the Captain’s toast. And no one on the ship is shown to drink (because they’re waiting for the Captain to speak) BESIDES Mark. And not only does he drink his glass, but he also drinks ours. Now, two tiny glasses of sparkling champagne are not going to do a ton of damage. To most people. But A) Mark has zero tolerance (for the show his character can drink, but still wouldn’t have a ton of tolerance) and B) he shotguns them so they’ll be more effective, quicker.
So basically, at LEAST in Pt.1, Act 1 he is the only person on the ship who is drunk. Which would explain his comedically high pain tolerance (limp noodle), why he thinks the initial looping might be a dream (blackout drinking), and why he’s ready to forgo all common sense and test the immortal theory and he believes the Captain’s every decision/plan and just goes along for the ride (he is our buddy on the mission because he is the most susceptible person aboard, even when acting like a superior pompous douche bag).
Or, you know, it’s past my bedtime and I’ve just seen the intro too many times to count. 
