Help. im feeling lightheaded, and dizzy?!

Help. im feeling lightheaded, and dizzy?

when i sit down just normally and then get up again, i feel really lightheaded and dizzy and sometimes my vision just like goes away for a few seconds [like turns white and i can't see anything] i even tried getting up slower and it still happened

1 week ago
i prolly don't get enough of the sugar. i recenly had to completely chenge my diet due to disease so i'm scrict dieting and i definetly get anough water everyday, i always carry a bottle around with me

1 week ago
it happens alot not just in summer

I used to get that quite a bit. When I would stand up I would feel dizzy. I wouldn't even stand up fast or anything, just stand up. And sometimes my eyes would be blurry for a little bit and it wouldn't go away. For me I think it was that I wasn't getting enough sleep, and my body was getting worn out and tired. I've been trying to get some more sleep in lately, and it hasn't happened as often since.