It began with a cramping sensation,

It began with a cramping sensation, but it certainly didn't end there.

The cramps ran through Sherlock's muscles, seemingly randomly, for about twenty minutes. Trying to ignore the peculiar sensation, which wasn't all that painful or debilitating, just annoying, he continued his experiments as planned. When the strange sensations stopped, he was relieved in a vague, distracted way.

Feeling as if his body had somehow set him back in the evening's plans, he talked Molly into going out for some fancy coffees for the both of them, just to keep her from hovering (and perhaps to see if he could, truth be told). She'd be gone fifteen or twenty minutes, at least, considering it was well after midnight.

Five minutes later, Sherlock doubled over, not even feeling his knees hitting the cold, hard floor as he clamped his teeth down on his lip to avoid crying out. It was as if every muscle in his body had seized up at once. Ripples of agony rolled through him, head to toe and back again, along with a sudden intense wave of heat that had him dripping wet with sweat in seconds. Tasting blood where he'd bitten into his lip, he finally screamed as his entire body felt like it was tying itself into one huge knot of sharp, unendurable pain. He passed out so suddenly that he didn't even have time to resist.