Headache. Headache and potentially low blood pressure which would cause dizziness, lightheadedness and if low enough can cause one to pass out.
Low bp and dizziness. Nitrates cause lowering of bp, which can cause dizziness and a feeling as if one might faint. It can also cause headaches.
Nitroglycerin. Potential side effects in people with or without heart disease are headache, dizziness, and a drop in blood pressure. The effect of the drug is only for thirty minutes.
Why?! This is a pretty foolish thing to engage in if there's no clear medical need. You can expect severe headache, hypotension, loss of consciousness, dizziness and racing heart. If you have an undiagnosed condition affecting certain organs, death could result.