Acid reflux, chronic sinusitis, sleep apnea and lack of sleep. Are they responsible for my dizziness and nausea?

They can be. Lack of oxygen can be a factor in all of your symptoms. Is the chronic sinusitis due to obstructions ( polyps) or a deviated septum? Has your sleep apnea been diagnosed by a witnessed overnight sleep centered study? If so have you been advised to wear a cpap? If so , are you? If not, in mild to moderate cases, a dental device can be custom made to reduce the obstruction.
Yes. Several medical problems can cause symptoms. Acid reflux can contribute to sinusitis. Acid reflux can be a cause of nausea loss of sleep due to sleep apnea can cause dizziness and high blood pressure losing weight often helps acid reflux and sleep apnea appointment to see an md is always needed with significant medical illnesses.