Is it normal that my fish float at the bottom of my tank?

My goldfish (RIP) did that for an entire 2 years of his/her life.
Fish losing their equilibrium and being unable to maintain their position is usually caused by swimbladder problems or swimbladder disease. This may result in the fish being unable to stay upright, swimming strangely or awkwardly and lying upside down in the bottom of the tank or in plants. Or the goldfish is floating upside down. Basically there is water in his swimbladder causing him to float from the swimbladder (which is underneith the fish.

If swim bladder disease does have an infectious cause, your fish will be better able to resist this infection (and others) if your water quality is good. Regular water changes and water testing are a must.
Pre-soak your flake or pelleted food. This will allow expansion to occur prior to the fish eating it, and will lessen the chance of impaction.
There is no cure for it. Feeding medicated food (see bottom of page), adding salt to the tank, feeding peas, and raising the temperature to 76 degrees may help but only for a short time. Eventually the fish may be unable to eat and will have to be euthanized (lol euthanize a fish).
You can also try to fast your fish for a few days - sometimes that can help.