There's no reason to believe Marco was unconscious for his lewd acts with Janna. You posted a screencap of one incident where he was unconscious, and we have no reason to believe anything sexual happened in that incident. But we have the word of God, Marco's voice actor as informed by his interactions with showrunner Daron Nefcy, telling us that when lewd acts happened between Marco and Janna (and they did), Marco consented to them. That precludes the possibility of him being unconscious during these acts, because as you noted, "hard to give consent while unconscious". It's an inescapable conclusion that Marco dicked Janna down, hard and often. He later forgot these acts, probably because she hypnotized him to (perhaps at his request, we don't know one way or the other).