Yes, and it grades high on them. Some sulfur dioxide forms naturally during fermentation, but most of it is added deliberately: at the press to stop oxidation, before bottling to keep the wine fresh, and in the dosage liqueur used to sweeten and top up the bottle. Pale sparkling wines get more of this protection than robust reds do, which is why they land at the higher end of the sulfite scale.

That pattern is far more typical of sulfites than of histamine. Sulfur dioxide released from the wine irritates the airways directly, so symptoms arrive within minutes and are respiratory: cough, wheeze, chest tightness, a stuffy nose. A histamine reaction tends to build more slowly and shows up as flushing, hives and a headache. Sensitivity to sulfites is most commonly reported by people with asthma.

As a category it grades moderate, not high. Most sparkling wine is made from young, pale base wine that never sees the long skin contact or barrel time that pushes red wine to the top of the histamine scale. Individual bottles vary a lot though: traditional-method bottles aged for years on the lees pick up considerably more than a fresh tank-method fizz, so the style you choose matters more here than with still wine.

Yes, and the label tells you exactly how much. Sweetness comes from the dosage added at disgorgement, and the terms are legally defined: brut nature has essentially none, extra brut and brut very little, while sec, demi-sec and doux climb steeply. If fermentable sugar is what upsets your gut, the driest end of the shelf is the practical choice, though it does nothing about the sulfites.