Electrical/Fuses problem?

Dodge Stratus Sxt 4dr 2005. The problem is when my car is traveling and I come to a stop such as an idle my car lights will go pretty much all the way out n then back in. It will consistantly do this when I have the heater or a/c on. After the lights go in and out sounds like a fan comes in my engine. Then once im home and turn my car off totally it sounds like a fan in my engine is on? Poeple told me its just whats charging my battery. The thing is all last night it was going on and off in my car ( the fan). So I go to turn my car on this monring and its totally dead. No electrical works at all. Why is this? Whats the fan doing and most importantly why do my lights go in and out everytime I come to a stop. The lights also go in and out when im driving but mostly when coming to a stop.