20Mustang00

Ok well a while back i had a problem with whenever i hit a puddle of water the lights inside would dim and then go back to normal. I have no idea what this is and havn't got it fixed yet but now i notice when i step on the break (only medium to hard breaking... ) The light will dim both inside and out for only a split second and after im stopped the rpm goes up and down not much but a little.. some time the car will start to shake, and the other day it went a little below 500 rpm's. Does this happen to anyone else?