After parking car it wont start. I have to turn headlights on then everyting goes on I start my car and the?

needles are all the way to the left & they're ticking and shaking like they want to move upwards but cant & then after a moment they go back up to their normal places. This afternoon everything went like that exept the fule gage this is the first time it stood at E and the computer said LOW FUEL even though I know I had more than half a tank in my car.As I started driving the gas needle went up slowly but is still not where it was before this happened. This (everyting except the Fule thing) is happening more & more it shuts off while driving and then turns back on by its self in an istant. I've taken it to my mecahnic & he's checked everything & says he cant find anything wrong with it. He says the he'd have to keep the car & see if it does it to him & then maybe go from there but every time I go of course the Car is running fine w/ no problems. Its a 2004 Murcery sable I bought in 2007. This started about 1yr 1/2 ago and only use to happen rarely but has become almost a daily occurence at this point. Has anyone ever had this happen to them?