I really don't understand your description of the tail curling up, from the tip, and then the sides..?
In any case, it does seem like your gecko is troubled. A better history would need to be provided before someone makes a guess as to what is wrong and why. Was this gecko always a poor-doer? How long have you had it, and it's tankmates? How is your husbandry (a loaded question, but you get the idea)?
Some things to consider;
While pedialyte is a good idea for animals that may be just beginning a downward trend, often when a gecko is found ill it is much beyond this point. Your description adds merit to this. Oral fluids may be too little too late, and IP or SC fluids should be administered. Even if the pedialyte does help hydrate your gecko it doesn't solve the problem your gecko may be having.
If you really want to help your gecko, it is time to take it to the most experienced herp vet in your area. Try www.arav.com and herpvetconnection to locate one if you are having problems.
At the very least, seperate this animal from the others to
a)relieve stress and competition from the healthier geckos and
b)to hopefully decrease any risk of your healthy geckos contracting any communicable diseases from your sick one.
c)if the vet is not an option (it is unfortunately a reality for some animals) then seperation allows closer monitoring, cleaner surroundings, and easier administration of such things as pedialyte.
Of course, whatever you end up doing, make sure to re-evaluate husbandry and seek any possible improvements as a sick herps needs the best environment available. Move temps up to the higher end of the prefered optimum temperature range. For example if your gecko's is 75-85 degrees, perhaps have it 80-88 degrees. This is short term only while your gecko is recovering.
Good luck with your little guy, I hope he pulls through 