Another reaction to fright or startle, is the freeze. Some will stay immobile for up to 20 minutes. Socially, guinea pigs are happiest in groups. Males may live together and usually will not fight once a hierarchy has been established. The happiest combo seems to be one male with several females, the male can be neutered or the females spayed to prevent unwanted litters.
Guinea pigs are messy housekeepers.
They spread their litter and food around, spit in their water bottle, and have a very opaque, creamy urine which may contain crystals. I would not count on it, and would supply vitamin C in the form of food supplements. Adding vitamin C to the water is not as good because the vitamin C quickly degrades in water and must be replaced every 24 hours. You can also never be sure how much they are drinking. Rabbit food also contains too much vitamin D for guinea pigs and may be at toxic levels.