Maybe I should have eaten something first

I took some Sudafed earlier today for this cold that I'm getting and I've been shaky all day. I had eaten some toast a little earlier, but that was all. When I started getting shaky I thought it was because I hadn't eaten in more than 6 hours. So, I ate. I'm still shaky. The only thing I can think that would cause it is the medicine. I hate this feeling. At least I can breathe and the sinus pressure is gone. LOL