lathargic rat

Question
In the past week my rat has seem to take a turn for the worst. He has lost a lot of weight and is week, he clearly hasn't been eating enough but he still seems interested in food it just seems like hes to weak to be bothered. He normally goes nuts for cheerios but lately hes been taking them and letting them just fall on the ground. I'm not sure that he has been drinking enough either, I have seen him drink but not often enough I imagine.
He also seems lethargic which goes along with him being weak , I feel like he wants to play and explore hes just too tired.
Could it be the heat? We try to keep it cool by not letting the sun in during the hot times of the day and we keep a fan blowing on low just in the room not on him.
We have been told to try soft cat food and fruits that provide him with water.
Any other suggestions?

Answer
It could be a combo of heat and dehydration. You need to get him to drink fluids. Stat with some childrens fruit flavored pedialyte and a dropper and get him to take some of that the best you can. Let him suck it out. He may just hold still and even hold the syringe while he sucks!
Rats dont do that good when its over 82 degrees.  Its vital they keep very hydrated...you can even give them watermelon!

A good idea is to take either empty plastic milk or juice jugs or empty soda bottles and fill with water...freeze them and put them in the cage. They will act as mini air conditioners, giving off cold air to the rats.

However, weight loss has me concerned. This could be from many things from kidney problems to heart disease or even simply from infection.

I would call the vet for a visit to be sure all is well.