。
When I stood up, I got dizzy.
Literal
Stood-up [conditional-たら] head [subject-が] was-dizzy.
くらくら is a 擬態語 (state mimetic) for dizziness or spinning — the repeated kura-kura evokes the sensation of the world spinning. ~たら marks a discovery: 'when I stood up, (I found that) my head was spinning.' A very relatable physical experience.