Hi, There are several possibilities but the more likely one based on the symptom of a feeling of heat and sensation of faintness (with vision dimming) which all occurred after standing for a moment highly suggests that your blood pressure had dropped to very low levels. Sitting down was the right thing to do to abort what we refer to as a vasovagal reaction. Causes include new medication (especially for blood pressure) recently added which is either too strong or interacting with other drugs, dehydration, not eating meals on time (hypoglycemia). You should talk to your doctor about any new prescriptions recently given to you in the past few days to few weeks either by them or even by some other doctor for a different problem. The cause of such problems is usually readily identifiable after reviewing your medications and personal health history and correctable. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Dariush Saghafi, Neurologist