I have been trying a few exhale dives to increase my tolerance to the pressure in deep water.
First time i did it i exhaled completely and duckdived. By 4m i felt my chest was going to implode and even my cheeks were being sucked in. It felt really really uncomfortable so i aborted.
I tried again and this time felt a little better at 4m but still quite bad.
On attempt 3 i hit a whopping 5.1 m
and managed to stay for 18 seconds 
Does this get more comfortable or does that feeling of imminent implosion persist.
How deep do you normally do these?
Do you exhale fully at the surface or on your way down?
Thanks
First time i did it i exhaled completely and duckdived. By 4m i felt my chest was going to implode and even my cheeks were being sucked in. It felt really really uncomfortable so i aborted.
I tried again and this time felt a little better at 4m but still quite bad.
On attempt 3 i hit a whopping 5.1 m
Does this get more comfortable or does that feeling of imminent implosion persist.
How deep do you normally do these?
Do you exhale fully at the surface or on your way down?
Thanks