Most hookah tobacco is moassel: shredded tobacco leaves mixed with molasses or glycerin and flavouring. The kind of leaf makes a big difference.
Blonde leaf (Virginia) is lighter and milder. It carries flavour well and suits long, relaxed sessions. Dark leaf is stronger, with more nicotine and a deeper taste, and is usually chosen by experienced smokers.
Masters often blend the two to balance strength and flavour. If you're not sure, say so: ask for something light, and mention it if you've felt dizzy before. A strong bowl isn't a better bowl.