Hi and welcome
Please have your boy vet checked, as always after a any major fall/blind jump.
Guinea pigs are prey animals and are afraid of wide open, exposed places as one of the results; they also don't have good far sight and cannot judge high levels so please only interact with a frightened piggy while sitting on the floor, where they cannot hurt themselves.
If they are on the freaked out side, it is better to just cover the cage top with a towel or sheet and leave them be to give their prey animal instincts time to gradually settle down; which may take a day or two.
Ideally, you use our whispering tips to make friends with your scared piggy and learn about how guinea pig prey animal instincts work so you can avoid triggering them as much as possible.
You can find lots of practical tested tips and advice in these links here, which we cannot repeat in every single post all the time:
How Do I Settle Shy New Guinea Pigs?
Understanding Prey Animal Instincts, Guinea Pig Whispering and Cuddling Tips
Here is lots more practical information for new owners to help them to a good start and help avoid scary situations like yours:
Getting Started - Essential Information for New Owner
Please also remember that it might take him some time to adjust to his new surroundings.
Make sure his cage is partially covered and he has lots of hides and tunnels.
Start by sitting next to his cage and offering food and talking gently to him.
You may find this guide helpful
How Do I Settle Shy New Guinea Pigs?