What could be the reason?

In the pass few months I have felt sick a lot more then I even have. I almost passed out at work twice. I got dizzy and I start shaking (like my hands).I also feel nausea often and have stomach pains. I have also lost a lot of weight for someone who has not been trying. Last I remembered I was 156 now I'm 128. Could I really be sick? What can cause this to be happening? I have my blood sugar checked and it was fine