2002 Vauxhall Zafira why is my car wobbling when i'm driving...

my car feels like its wobbling when i'm drivin, it started about a week ago, sometimes its worse than other times, its more noticeable when i'm driving quite slow for the gear the cars in 'for example 25mph in 4th gear' it was wobbling that bad the other day i thought a wheel was falling off but it eased off abit further up the road, also since this problem started my brakes dont seem too good and (i think) might be slightly grinding, and each time i start the engine up i have to rev it a few times or it will just conk out and then when i stop the revs are slightly higher than usual, these issues all seem to of started at the same time. and also a week or two earlier my heaters in the car were blowing cold air and water was coming from the radiator so my brother put some sort of sealer in the engine and it did the trick the heaters are fixed and it stopped leaking water, just thought it might be worth mentioning this last part incase its all linked. has anyone else had these problems or have any idea what it could be wrong ??