Getting weirdly light headed

ok so i just relapsed big surprise and it was not very deep like i only did a few and they were all like barely even styros one was kinda deep but not really. anyway i was standing up for whatever reason and i was like fine for a second and then BOOM i couldn't see and felt like i was about to pass out and die. i don't know why this happened it's so weird and like it's never happened before so idk maybe i just haven't drunk enough water today or something but if anybody know it would be nice if u could help me out. :PP