I Have Had A Couple Episodes That End In A

I have had a couple episodes that end in a near fainting. I get very sweaty, dizzy and can't seem to cool off. One episode I fainted, another I vomited but after an ER visit (after fainting) nothing obvious was noted. ? I had a stress test, negative. I have high BP, fifteen years on 20m lisinopril. I have developed tachycardia over the years, doesn't seem to be mechanical. Ideas on what to check?
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