Driving in my 2003 Ford Focus today and it overheated, the reservoir was empty as I hadn't checked it in a while. There was no warning beep, a light had come on but the first I noticed something was wrong was because it had lost 90% of its' power. It was still revving hard but was going hardly anywhere. I thought I had fucked the gearbox til I noticed it was overheating. I parked up and walked the rest of the way home and let it cool down for a few hours. When I went back everything worked sweet. Is this a mechanism of the car to let you know it is way too hot or something else I should be worried about?