I've been dizzy on and off. tonight i had black spots infront of my eyes, ears ringing and profusely sweating while standing. what can cause this?

Sounds vasovagal: Which means sounds like your blood pressure suddenly bottomed out when you stood up. Did you feel immediately better upon lying down on your back? Did you get a headache as well? Causes of vasovagal attacks could be dehydration, low blood sugar, low thyroid function, low adrenal function, dysautonomia (probably less likely in your case), heavy periods, medication side effects. Check with doctor