goldfish ailment

Question
Hello, i have a fantail goldfish that i have had since 2001 he is in the same tank and he is the only one, it is a undergravel system and the chemistry is all ok i have the strips that check everything,
Up until about a month ago my fish was perky and always going crazy at the surface at feeding time, in fact he would make smaking noise when he was hungry, now he is lazy, he eats when i put food in but does not go crazy like he used to, i tried some peas thinking of constipation but that did not help, and the bowels are moving, i was thinking of the egg binding issue if it is a female but i dont know how long it takes for the body to reasbord them?  
also the fish is scared easily he darts back and forth quickly, he does not have any obvious signs of anything like dropsy either, any ideas?

Thanks so much

Answer
Hi Marc;

What size tank is he in?
What kind of filter?
How often do you usually change his water?
What is the temperature of the water?
Have you moved recently or changed the room around where his tank is?
Do his eyes look like they are beginning to protrude slightly?(hard to tell sometimes)
Have you changed his food, water conditioner or anything else?

Let me know as soon as you can.....

Chris Robbins