Headaches as well as stomach pains are classic signs of nicotine poisoning... sounds scary, but trust me you are not going to smoke yourself into a coma.
All the advice given about full stomach, not being in the hot sun, being hydrated are all helpful.
One tip I will add is to consume something with a HIGH sugar content - this will almost immediately counteract the effects of the high nicotine concentration. Soda, candy bar, whatever - it will make you feel better inside of 5 minutes almost every single time. This is actually the reason why PORT has historically been considered a good pairing with cigars - back in the 19th century many cigars were much much harsher and stronger due to inadequate fermentation and the drinking of the fortified wine with it much higher sugar levels would help to counteract the excessive nicotine levels.
Hope this helps,
STS
CEO, DE