[Mullins]

Sounds like mild lung squeeze, i.e. your chest is not flexible enough for those depths yet so blood vessels are rupturing. It often takes a while to get used to exhale diving and going straight down to 8m might be a bit much to begin with.

FRC diving can be safe when done properly but there are also plenty of ways to get it wrong and put yourself in a dangerous situation, possibly more so than with inhale diving. It's probably not a wise thing to be trying if you're on your own.