hi, thank you for your query, what your experiencing is called as Pre-Syncope. Its a prodromal state that often includes dizziness and loss of vision ( blackout ) (temporary), loss of hearing (temporary), loss of pain and feeling (temporary), nausea and abdominal discomfort, weakness, sweating, a feeling of heat, palpitations.. in most patients it usually leads to loss of consciousness there are three main causes for it- cardiogenic, reflex and orthostatic hypotension other forms include vaso-vagal syncope,orthostatic syncope the basic mechanism in any form being decrease in blood supply to the brain for a short period of time. a full physical exam should be done to pinpoint the cause the following investigations can be done- 1.complete blood picture 2.ecg,echo 3.tilt table test 4.stress test these should be able to clinch the exact diagnosis.. thank you, you can contact me for any follow up questions