Do allergies cause dizziness and fatigue?

Oddly enough, yes. My allergist says it's pretty rare, but some people react this way to allergens. I tend to react this way to peanuts, chlorine, and my allergy injections, but my reactions change over time: hives one year, sneezes the next. :-P Allergies are strange, strange things.

Recent studies have found that in some allergic reactions, blood pressure can take a steep dive. That would explain the dizziness.

If this always happens in the afternoon, what are you eating for lunch? Or is there a place you spend your mornings that might be musty, dusty, or near certain plants or animals? When you have a consistent reaction pattern (every afternoon, for you), it's a clue to hunting down the problem. If you feel fine on weekends, for example, maybe there's something you react to at work, or the breakfast or lunch you only eat on workdays.

Good luck!

Of course. I have bad allergies.