Seeking Advice for Frequent Fainting Episodes - Any Insights?

hello! I don't think I've ever actually fainted before but I don't know any other medical term for what I've been experiencing the past year! I plan to talk to my doctor soon but I was wondering if anyone else has had a similar problem or knows anything that helped for them? They've been getting more frequent and increasing in intensity and duration but I have these times where I feel very light headed and it goes away if I immediately sit down, but if I don't sit I feel blood rush to my head and my vision turns black and my knees buckle! When I finally do go down after my knees buckle I feel my body pulsing with blood and sometimes hear a ringing in my ears and have to stay down until everything goes away (including my darkened vision). I've been taking multivitamins everyday for awhile and when I'm late to taking them I'm likely to have this happen or I at the least feel weak and groggy. I was diagnosed with anemia in 2018 but I had recent blood work confirming I no longer do so... if anyone has any insight to offer at all it would be greatly appreciated!! thank you so much for your time and have a great rest of your day/ night depending on when you see this :P