Is it possible to have reverse altitude sickness?

No: If by that you mean you have come back to lowland and yet have nausea, headache, dizziness, loss of appetite, fatigue, look for another cause. Altitude headache by itself should resolve at low altitude by 12 hours. If you have shortness of breath or cough- high altitude pulmonary edema can persist up to 48 hours after returning to low altitude. Go see your health provider.