Sudden drop in power??

It sounds like your computer has put your engine into "Fail Safe" mode for some reason. It's trying to protect your engine from catastrophic failure. It could be running at too high temperature or it could be an oil pressure issue or not enough fuel coming in, which could burn valve seats. Did service engine light come on ? If there was no light, I would check my oil and coolant levels ( after it cools down ) and if they are okay, I would disconnect the negative side of the battery for about ten minutes. This allows the computer to reset in most cases. If the same scenario happens, you will need to have it diagnosed by a mechanic with the proper electronic tools.