What happened??? I felt like I was going to pass out?

Just a few minutes ago I was having a cig outside and when I stood up I was suddenly overhwhelmed with a feeling of faintness. My vision even got a little blurry and I started shaking. I was really scared and thought I was gonna pass out. I didn't eat the whole day until the moment, but in the past I didn't eat for a whole day and didn't feel like that. What happened this time??? I still feel a little shaky even though I ate 2 slices of pizza and drank some tea.