Car almost stalls; radio, headlights flicker
I drive a 2000 Focus SE with 17K miles. A couple of times per 20 minute drive, the car will lose power like it's about to stall. At the same time, the electrical functions like the radio and the headlights lose power as well. When it occurs, the engine revs loudly and it feels like it's putting out too many rpms on a low gear. This happens for about a second and then it's back to normal. The car has never actually stalled.
I checked the battery and it reads 12.8V when the car is off and 14.95 when it's on and idling. I don't know what else I should check. What could be the problem? Please bear with me; I am not very knowledgeable when it comes to cars!