Thank you for getting back to me so quickly! I am not in the habit of laying still at any point in my dive, I am always either finning or at least facing the surface so I can move my arms and check if anyone is swimming above me before I surface.
It was actually pretty comical during my training session today because our pool has several different groups and classes using the various areas at any given time without necessarily being on the schedule. Anyways, there is a group of ladies doing some aerobics in the deep tank wearing those float belts. Myself, being on limited time before work decided to say screw it and just continue my diving while swimming underneath them. I figured a 5 foot tall woman floating in 14 feet of water leaves about 9 feet of usable space underneath for me to hang out. So as I'm going under on my last dive I swam straight down the wall, up the drop off slope, and then down and out the first lane. When I finally popped up on the other side by the stairs I hear giggles and a couple of cheers from said group of ladies. Thankfully, the morning crew seems pretty relaxed.
Long story short, when you have on bright white fins and are female there are eyes on you lol! But our pool is mostly at your own risk so thankfully I don't have to deal with any micromanaging.
I have not trained any sort of exhale diving but I have done some buoyancy experimenting in the past in a similar dive tank (~3.6m) by allowing myself to sink naturally by exhaling at the surface. Keeping empty lungs all the way to the bottom was never uncomfortable for me, it was the first inhale upon surfacing that felt mildly painful (due to the sharp expansion/break of suction I think). Thankfully I think my thoracic cavity is pretty flexible (singing, dance, yoga, and swimming from young age) and I learned to frenzel equalize (surprisingly!) pretty naturally without thinking about it too much (think TOO MANY childhood plane trips).
Now I will say that when I am doing these 4m dives I have about 1.3kg on my waist to help me level out and maintain a more relaxed descent, and I know that being weighted increases the risk of any situation. I feel comfortable enough at my ability to take that risk (my belt also has a clip that can be released quickly) and make sure that I'm learning with correct technique but I am wondering if there are any considerations I should take with that out there? That's why I limit my dives to >:45 secs even though I can go for much longer comfortably.