Syncope is defined as a sudden loss of consciousness due to sudden and transitory hypotension (low blood pressure). Syncope disturbs brain perfusion. Neurocardiogenic syncope (also called vasovagal syncope) is one of many types of loss of consciousness due to low blood pressure. The blood flow in the brain reduces and loss of consciousness occurs due to low blood pressure. Before losing consciousness symptoms like blurred vision, dizziness, weakness, nausea, etc. can be present. Normal blood pressure is defined as a systolic reading within the range 90-130 mmHg and a diastolic reading in the range 60-80 mmHg. Low blood pressure is defined as blood pressure 20 mmHg under the USUAL values. This means that a reading that is low for one person can be normal for somebody else.
According to the etiology (cause of low blood pressure) there are generally 2 types of syncope:
I. NON-CARDIOGENIC and
II. CARDIOGENIC
Non-cardiocenic syncope includes several types:
1. NEUROCARDIOGENIC (VASOVAGAL) SYNCOPE. – Neurocardiogenic syncope is due to an abnormal response of the neurvous system (sympaticus and parasympaticus) to an outside trigger. During the response, the parasympaticus becomes overactive (it overcomes the sympaticus) and can cause vasodilatation and decrease in heart rate (bradycardia). Vasodilatation and bradycardia themselves cause low blood pressure (hypotension) and loss of consciousness. A person who experiences vasovagal syncope recovers very quickly (in a few minutes at most). There could be many triggers for vasovagal syncope: emotional distress, including panic attacks, anxiety attacks or fear; standing in a hot, crowded area; having a bowel movement (especially if straining); coughing strenuously; unpleasant situations, such as the sight of blood; urinating; standing in one place too long; breathing too fast (hyperventilation); severe dehydration; severe pain, and heat exposure.
2. ORTHOSTATIC SYNCOPE – Orthostatic syncope is also caused by an improper response of the nervous system. During this type of syncope, the sympaticus nervous system fails when the body comes into a straight position.
3. CEREBROVASCULAR SYNCOPE – Cerebrovascular syncope is due to a brain insult.
4. EPILEPTIC SYNCOPE – Eplileptic syncope is due to seizures.
5. SINUS CAROTICUS SYNDROME – Sinus Caroticus Syndrome is due to hypersensitivity of the the sinus caroticus found in the carotid artery. An overactive sinus caroticus causes vasodilatation and bradycardia that leads to low blood pressure. Pressure on the sinus caroticus during shaving, wearing a tight tie around the neck, sudden neck rotation, etc. can stimullate the sinus caroticus to overactivity.
6. MEDICINAL SYNCOPE – Medicinal syncope is due to the side effects of many medicines such as: anesthetics, anti-anxiety drugs, antihypertensive drugs, drugs for treating coronary heart disease (CHD), diuretics, heart medicines, some antidepressants, narcotics, alcohol etc.

CARDIOGENIC syncope is due to a heart disorder:
1. Valvular disorders;
2. Heart attack;
3. Congenital heart diseases;
4. Lung embolism;
5. Heart arrhythmias, etc.

Finally,it seems that there is some confusion in your question because two opposite disorders are mentioned in your pre-existing conditions: hypertension and syncope. Anti-hypertensive drugs can cause syncope if not used properly.