Third person
Sans woke up staring at the ceiling, he could feel a small body laying on his chest, he wiped his face with gloved hand ... WAIT WHAT!? Sans suddenly bolted up, looking down to see Papyrus' tall lanky body with himself resting on it, he presumed that was Papyrus but just in case he didn't use a name "Sup, hey um, dude? Can you wake up ?"
Papyrus' POV
I woke up, a large body shifting underneath me, I slowly opened my eyes looking at whoever was under me, I was lost for words ... It was me! "OH MY GOD, SANS HELP A DOPPELGÄNGER!"
"No no bro it's me Sans!" I looked at him with pure fear in my eyes "oh and pap look down" he said simply. I slowly looked down seeing sans' body, while Sans was in my body, Sans was laughing "UM SANS? WHY ARE YOU LAUGHING ?" "Your reaction to this" Sans was tearing up at my reaction
Third person
Sans and Papyrus were looking at each other/ themselves "S-sans" papyrus said calmly "Yeah pap ...?" Sans said blushing a small orange glow "oh my stars he's cute" papyrus thought "WAIT, he's my brother AND at the moment he's ME! Ugh I really can't be thinking about this" Papyrus was blushing a bright blue "Um Pap why are you blushing ... As I'm usually in my body I KNOW that's a blush ..." Papyrus was staring at Sans with small hearts in his eyes "Um it's nothing Sans ... Anyway why do you think this happened?" "I'm not sure I was asleep all the time I was home yesterday."
Papyrus remembered the man from the alley ...