Sinking in Whale Eye

When I was doing the Skate lesson, I felt like I was doing OK, staying pretty balanced. And the Nod lesson seemed to go OK after getting used to rotating my head laterally instead of lifting it. But today, I started working on Whale Eye and found that my first head rotation goes OK, but when I try to rotate my head next time around, my head is too far underwater for one of my goggles to peep out.

After breaking it down into small movements, I realized my torso/hips are sinking and bringing everything else with it. I'm trying not to overkick to compensate, but that's what I instinctively want to do. I've gone back and focused on keeping my forward arm low and relaxed, keeping my core engaged and keeping my head down in a level, relaxed position, eyes down.

Any thoughts on this? After reading another forum, I'm wondering if I'm letting my breath out too quickly and losing some buoyancy.