What is up with my gas guage?

I have a 96 VW Jetta. Recently the spedometer has been on the fritz.. it will work sometimes others it won't work at all. There are sometimes even when it bounces around - spooky. ha! I can deal with that and guess at how fast I am going. But now the gas guage has started going haywire. I filled it up yesterday and it has been working fine since but before that it was under half a tank and was bouncing around between half and empty all the time. It seems like it sways with the curves I take. It's only doing it when I am under a half a tank of gas tho... What is going on?