My rabbit is a young male Lionhead who was completely normal and acting like himself the…

My rabbit is a young male Lionhead who was completely normal and acting like himself the night before this happened. He was out of his cage, moving around normally, and I did not notice any limp or problem with either back leg. The next morning, he immediately went underneath my bed and stayed there for most of the day, which was unusual for him because he is normally very active, playful, digs, tries to escape his cage, and wants to be around me. At first I thought he was hiding because his litter had been changed and my cats were acting differently, but when I shook his treat bag he came out and ate normally. That was when I noticed that his left back leg looked slightly abnormal. Later, when he came out from under the bed, I noticed that he was limping and avoiding putting much pressure on the left hind leg. He does not seem completely unable to use it, but he usually lifts it up instead of putting normal weight on it. When he is sitting, the leg sometimes appears to angle slightly toward the left, and the area that seems most abnormal is around the lower leg/knee area closer to the paw. He can move the paw and toes. He can stand, turn around, stretch both hind legs, and he has voluntarily hopped several times. He even hopped into his litter box normally, and he has tried to hop out of his cage toward me. He is still eating, appears to be drinking, is producing normal-looking poop, and is grooming himself normally, including grooming the affected leg. He has also been able to stand and move around without falling over. When I first picked him up to show my dad, he kicked while I was trying to hold him and made a small whimpering/crying sound, but I immediately put him down and I have not noticed him crying when he is simply sitting, eating, grooming, or moving on his own. He has not been constantly screaming or showing obvious severe pain, but he is much quieter and more still than his normal personality. He normally spends a lot of time digging, playing with toys, trying to get out of his cage, and hopping around, whereas now he mostly sits, eats, uses the litter box, grooms, or rests. His breathing also seems somewhat faster than normal while he is sitting still, although I am not sure whether this is from pain, fear, or stress. The symptoms have been present since approximately 7–8 PM and have stayed about the same or possibly improved slightly rather than rapidly getting worse. There were two awkward incidents around the time before I noticed the limp: the day before, I dropped him from the bed and he landed somewhat on his side, although it did not seem like a hard fall and he acted completely normal for several hours afterward; there was also a later slip/awkward landing when he hopped off a small platform. After the second incident, he was still able to hop and move, but I became concerned about the leg. I have now put him in his cage with fresh bedding, hay, food, water, litter, and toys and am keeping him confined so he cannot run or jump. The cats are being kept away from him. I have not tried to straighten, massage, or splint the leg. I am trying to determine whether this could be a sprain, fracture, joint/hip injury, or another problem and whether he needs emergency care tonight or can safely wait for an exotic/rabbit veterinarian tomorrow. I am especially concerned because he is clearly avoiding normal weight-bearing on the left hind leg and is quieter than usual, but he is still eating, pooping, grooming, standing, stretching both hind legs, moving his paw/toes, turning normally, and voluntarily hopping