For @merelypassingtime who had an extremely valid headcanon to go along with mine:
Headcanon: The first time Mycroft woke from a nightmare was the first time he heard Greg sing. He was so shocked at how good his voice was that he forgot what he had been dreaming about and settled down peacefully.
Mycroft gasped loudly as he woke abruptly from a horribly vivid nightmare that involved way too much blood to not be completely unsettling. He lay staring at the ceiling while he tried in vain to calm his racing heart.
His hands, that were clutching helplessly at the covers across his chest, were suddenly taken in warmer hands, gently pried apart, and tugged until his whole body was pulled onto his side. He was now facing a sleepy Gregory. The other man was smiling kindly at him but there was a glint in his eyes that made Mycroft forget his terror in favour of suspicion. He narrowed his eyes at his love and his eyebrows creased in confusion.
Greg’s smile grew wider and a small huff of laughter escaped him before he began singing.
“Never gonna give you up. Never gonna let you down. Never gonna run around and desert you.”
Mycroft gawked and it took him a moment before his complete shock had him in stitches, laughing at the idiot in his bed.
“Never gonna make you cry. Never gonna say goodbye. Never gonna tell a lie and hurt you.”
He had no choice but to pull Gregory into a kiss in order to shut him up and stop the nonsense. He pressed their lips together until Greg stopped laughing enough to kiss back. When they pulled apart they were still both smiling stupidly at each other.
“I can’t believe you just rick rolled me. In bed.”
“I can’t believe you know that I just rick rolled you.”
Mycroft shook his head in amusement and lay his head back down on their now shared pillow. “You are a ridiculous man.”
“That I do.” Mycroft replied and then they both let the silence stretch until they fell back into a much more restful sleep.