Not strange at all if your trying out for a SRT/TAC/SWAT/SF team. Pretty run of the mill actually. My advice do it a few times with full advantage. Meaning just goggles and bathing suit. Do this first a couple times to get used to it like this. Relaxation is huge and DO NOT hyperventilate yourself. Breath normal before you dive down, take a deep breath and use the walls to your advantage. Breaststroke is the best way to tackle this. Watch and rewatch on YouTube the proper pullout and streamline methods for this will be what helps you get this done fastest. When you re confident and comfortable doing this then and only then add pants, then shirt, then gear. This is my opinion and comes from my experience as someone that has lived in this environment all my life. Water is where I work and play. Relaxation is key. You'll find sooner or later that being comfortable and relaxed in and under the water will make it very easy to go 50m and or much more. I can personally do 75m with no issues.
The exact routine I follow is :
Laps ; 4x front
4x side/rescue
4x breast
4 x back/ elementary for warm up
2 laps underwater at 50% , just relaxing myself and getting my breathing down..
5 laps pushing a 20lb brick underwater .. Everytime you need to come up for air I'm taking 2-3 deep breaths and going back down ( is this a mistake by not letting myself fully recover ?)
10-15 mins of treading water 1 min no hands , 1 min no feet , on and off ..
dround proofing for 3-5 mins
Max out tread time with the 20 lb brick / swim the bricks back to the other end of the pool