Thank you for choosing HCM.
As you mentioned you have dizziness
, alongwith fast heartbeat and sweaty palms especially during prolonged standing.
Most likely you are suffering from whats called vasovagal syncope or presyncope
which means due to prolonged standing especially when you are dehydrated like skipping a meal/breakfast or standing under the sun for long, your body is not able to compensate and maintain your blood pressure and your blood is pooled to your legs and you start feeling dizzy and lightheaded and may end up fainting
Simple things you can do to minimize these or prevent these:
Drink plenty of fluids and eat more salt. Atleast 10-12 glasses per day.
Make sure when you have to stand for long durations, that you are moving your feet or squeezing your calf muscles to keep the blood flowing back into your heart. Donot skip meals.
Having said that, if you have suddenly fainted without any warning signs especially during exercise or suffer from palpitations even at rest or have chest pains, or any previous heart problems or your symptoms donot improve with the simple measures mentioned above, you should be seen by a physician immediately and he might suggest to get and ECG of your heart done. Also you can get your blood pressure measured at your physician's office.
Hope this helps.