YOu've gotten great advice so dar, but I have some questions/comments:
Being smaller, they'll have much more rapid heartbeats as long as they're not too cold. So yes, a rapid heartbeat can be a sign of stress, I agree to make sure he has adequate hiding places.
Mine loves paper towel tubes.
Do you know if your gecko was wild caught or captive bred? Most wild caught specimens will not be as expensive, but can harbor parasites and that can affect their appetite.
Do you have a good reptile vet lined up?
If not, try
ARAV redirect
or
Herp Vet Connection and find your state for the nearest exotics/reptile vet.
What substrate is your gecko on?
I always keep new animals on paper towel for about a month so I can monitor their poop, and its easy to clean.
That way, if they have parasites, its easy to keep the cage clean and sterilized until they're treated as well.
If you can get a fresh poop sample (if it's still wet, ziplock baggie it and put it in the fridge) to take in to the vet it'll be cheaper and less stressful for the animal rather than bringing the gecko into the vet with you.
fecals run anywhere from 20-50 bucks depending.
Good luck, these are fast and vocal geckos, but they are really a lot of fun and very rewarding to keep!
Can you get some pictures?
