Getting slightly light-headed can be pleasant. Nicotine toxicity, on the other hand, is unpleasant, causing nausea, diarrhea--won't kill you, but you might wish it had. If you feel a nicotine o.d. coming on, a spoonful of sugar or honey may reduce the symptoms in fairly short order.
Now here's the funny thing: Burleys have more Vitamin N than Virginias, but if I smoke a straight burley, I fare far better than when I smoke a straight Virginia. And some tobaccos that are rated "mild," (and I assume nicotine is one of the factors,) give me a heavy buzz. e.g., Pease's Piccadilly is rated as a mild tobacco, but I just can't smoke it. I like the taste, but it does terrible things to me. Go figure. Ditto for Early Morning Pipe. I smoked Balkan Sobranie for many years, and when they quit making it, switched over to other similar blends. These days I find myself sampling some aromatics, something I thought I would never do. Two reasons: I can't find an English/Balkan blend that seems to agree with me these days, and second, I've recently developed a taste for some of the milder aromatics, such as the Mac Baren 7 Seas series. Ain't no accountin' for taste.