2002 Buick Century car speedometer goes off and on by itsel

My buick century custom's speedometer, fuel gauges flicker on and off by itself and stays off for a number of days and then if i hit a bump or something it will snap back to normal. Also when this happens all my service lights will come on and stay on. like service engine, auto lock, etc. But I am not sure if this a mechancial issue or something to do with the electrical system. So therefore, it is long periods of time where i don't know how fast I am going or how much gas I have in the tank or the temp of the engine. I also noticed that the miles don't change on the vechicle when this happens.