"feelings of dizziness and being lightheaded" sounds much more like a tourist was walking around Italy in the summer with a heavy backpack and not drinking enough water after getting off an airplane and probably impinging too much wine at dinner the night before.
Same with any hotter climate tourist location and 'mysterious syndrome'.
Also combine with perhaps a little change in their stomach biome from drinking different water and/or eating different dairy products, making them more easily dehydrated.
People tend to either over or under indulge while traveling too (I always lose weight when I'm on the road myself) and that's never awesome in either direction