My son has vertigo, is nauseous but minimal vomiting, sweating but no fever, lethargic and has a loss of appetite. blood cell counts are fine.

Unwell: No very clear context. Can you be more specific please. Review with doctor if your son is unwell . Sounds like he may need examination.

Many possibilities: Could simply be a migraine or a viral illness. However early in an illness a blood count may be normal and rise later. Can be a very nonspecific test, plus don't have a lot of details about your son's age or history etc. Safest to see a doctor licensed in your area for re-examination and urgently if persistent vomiting, severe headache, drowsy. All the best.