Hi Hales
Most anti-depressants can make you feel a bit weird for the first few weeks, this is normal whilst your body is adjusting to them. What is happening is that the dizziness and on/off nausea is causing you to worry. If you can ignore them and tell yourself they are transient feelings, nothing more, they will pass. With anxiety we get anxious over the symptoms of anxiety and tell ourselves "this is awful, what does it mean? There is something really wrong!!" and then we get worse.
if you can try and relax when you feel dizzy (you will not faint) and when you feel nausea (you will not throw up) and not attach too much meaning to them, then that will help.
If the symptoms get too much, then as Hibee says, go back to your doc. There are lots of different SSRI's to try and sometimes you have to try one or two before you fid the right one that suits but it is normal to have your described symptoms at first, they usually pass. Good luck!!