how do i not get fuckin wiped at the blood donation. i gotta go do it tomorrow and sometimes i come out of it fine and sometimes im ttruggling to not pass out on the bus home

how do i not get fuckin wiped at the blood donation. i gotta go do it tomorrow and sometimes i come out of it fine and sometimes im ttruggling to not pass out on the bus home
food and water. like literally eat/drink more both before + after getting a lot of blood drawn and you'll feel a lot less like death