The problem may be Jimmi is too cold. Dragons cannot Thermoregulate their body temperature, so thet need heat lights which is the basking lamp to help them. The temp in the basking area should be 105*F-110*F, on the warm side the ambient temperature should be in the 90's and the cool side mid 80's. Without this heat a Dragon will shut down and sleep and cannot digest the food. They need to have their lights 12-14 hours a day. Along with the tank being too cool the stress can add to the inactivity. I would get the Basking and UVB light on and get him warmed up asap.
To prevent dehydration, you can give a 20 min soak in warm water and an infant eletrolyte solution. In the US we have Pedialyte and in the UK there is Dioralyte. It needs to be mixed 50/50 with warm water and while in the soak, you can gently rub Jimmi's abdomen to help promote a bowel movement. The soak will also warm him up. Reptiles absorb fluids through the vent area.
I want to go over diet with you: Collard greens, mustard greens, dandelion greens, escarole and curly endives. Butternut squash and various berries are great for a treat. The Veggies should be put in fresh daily, and done about an hour after lights on. They need 20% veggies daily and 80% live prey under a year of age and over a year the percentages reverse.
The live prey should include crickets, silk worms, roaches, goliath worms and phoenix worms. Meal worms have little nutritional value and arehigh in chitin which is the outer shells and can cause a blockage.Super worms and wax worms are like giving the Dragon candy. All veggies and prey should be dusted with calcium daily 5 days a week and vitamins 2 days a week.
If the problem continues after you do the heating and lighting revisions, I would have a Fecal done by a Reptile Specialist and rule out any parasites that may have been brought on by stress.
I really suspect that once the temps are raised, Jimmi should respond and start perking up, Please let me know if you have further questions. My goal is to give you 100% excellent service. Joan