Background:

Just getting back into exercise again after a few years (about 3) of not really doing anything very vigorous at all - mainly just walking/small hikes, sometimes a kayak and a swim. Not completely sedentary but definitely not as athletic as I used to be.

I signed up to the gym, and everything seems like its going well. I'm fine doing a "warm up" on the treadmill for about 10 minutes, including some stretches in my arms etc while walking. I start doing a little lifting/squats/crunches type strengthening training and I immediately feel very nauseated and I have to go sit in the restrooms for a little while until the feeling wears off. I'm not really doing anything extremely strenuous either!

Is this just because I'm not used to exercising and my body has to condition? Should I see a doctor about this could it be something serious? or maybe I'm not eating enough prior to exercising (I had a boiled egg, half a mango and a cup of coffee before going in). Nutrient deficient perhaps?