Disclaimer: I am a very unfit 42 year old vegetarian sloth. 
I had my first training session with a personal trainer at the gym near work today and while I (mostly) enjoyed the weights, I felt light headed and a bit sick straight afterwards. I suspect I hadn't eaten enough beforehand (having read about the perils of eating before working out, I erred on the side of caution). I felt off for most of the afternoon, even after eating.
Is there a way to avoid this feeling? I suspect I will be full of aches and pains tomorrow but I can cope with that - not sure I'd keep going if I am going to feel faint and sick each time though.
Reading online, advice varies about how much and when to eat before training so any advice that's worked for you would be appreciated.