Can you still faint if you are sitting down with lock knees?

Faint. Fainting is due to decreased blood supply to the brain. The effects of gravity are greater when standing than sitting, so fainting is more likely standing. But it can also happen in a sitting position, even with the head down, if the brain is not being adequately perfused by blood. This might be for a variety of causes related to heart, brain or even , possibly emotional.