Why does my goldfish not move Dying or lazy

My daughters goldfish hasn't really moved for the last day or so and just sits at the bottom of the tank. Is it dying or just lazy??

Your fish might be overeaten, bad water condition or easly too small tank to swim. Check parameters of water such as the temperature, pH, the level of NH3/4 (keep 0% - it'is toxic), NO2 (keep 0% - it'is toxic), NO3 (can't excide 40mg/l) and if your filter is regulary washed and water changed (25-30% water of a tank at least once a week - depending of the tank size and fishes size, and also the number of fishes). Water ought to be properly prepared before changing: with the same temp. and pH (acceptable tolerance is +/-1 degree) as the same in the tank - these are basic conditions to keep the fish healthy and vitality.

Regarding NO2 - plants need this compound to get N mutch easier then directly from NO3 to rise, therefore, when there is lack of NO2 in water, plants change NO3 back into NO2 compound during photosynthesis and then they pick the N up and return O2 into water - so don't worry if you have got trace of NO2 in your aquarium with plants. Also they take the N from those previous two mentioned compounds: NH3 and NH4 (very toxic for fishes) eliminating in this way the toxic compounds from water. Fast growing plants very help to filtrate the water from unvisible poisons coming from uneaten rests of food and fishes excrements. If you provide plants in your tank with the proper light and number, especially with CO2 supply (not forgetting about fertilizing etc.) you should not worry, but check water with specialised tests commonly available in pet shops.