Image imported from derpibooru 
Original Description:
 
He just felt peaceful. Also strangely safe for some odd reason. His body tingled as a warm feeling came throughout his body as Sonic took long slow deep breaths from the blackish grey rubber like material anesthesia mask on his muzzle as a advanced alien anesthetic/oxygen mix flowed through the hose and mask filling his lungs. The alien anesthetic machine had a black rebreathing bag on it as it inflated and deflated with every breath the blue Pegasus Stallion took and the two tanks containing the oxygen and anesthetic hissed as they let their contains flow into the captured stallion.
 
Sonic looked around the lab a bit still breathing the gas from his mask before his eyes began to feel heavy. His eyes sight began to get blurry a bit as thing started to get hazy. A surgical light soon turned on as light shined on Sonic who felt numbed and helpless to do anything as he was restrained and unable to fly or run away he was at these aliens’ mercy. But if were they going to harm him then why was he hooked up to anesthetic machine breathing in gasish anesthesia and was beginning to fall into twilight as he melted breathing from the mask.
 
Several seconds later humanoid aliens wearing surgical gowns similar to what human surgeons wearing in operating rooms on Earth entered the room. 3 of them went to check the equipment while the other 3 came over to observe Sonic who was bearly able to see anything as his eyesight was completely blurry now thanks to the gas and his ears were ringing and could only hear his own muffle breathing as one of the aliens took his left foreleg and rubbed it making him feel more relaxed as he started to drift off to his medically induced sleep.
 
Sonic tried to fight the gas, but it was far too late as his entire body was numbed. His green eyes fluttered as they got heavier and sleeplier. The blue Pegasus’ eyesight started to wave around like water in the sea. Everything in his mind was numbed and only one thing came into it as his eyes got heavier each passing second. ‘Sleep’
 
Finally after trying fighting the anesthetic Sonic stopped fighting it and his eyes closed as his entire world and mind went to sleep with the only sound of his breathing as he fell into twilight. Sonic’s fate now rested in the aliens hands as they began to prepare to extract a tissue sample from the sedated Stallion.