Game Mechanics: you are constantly pushed underwater unable to feign death

[Videri]

As long as your X and Y coordinates don’t change, you should not be interrupted except for stuns. You should be able to sink straight down along the Z axis, assuming you’re not being hit, and cast any spell. If being hit, use a corner and you should be able to cast. You can also try to correct for push by swimming against the direction of push and crossing your fingers.

It’s all about X-Y displacement.

Furthermore (and I believe you already know this, Chortles), when people try to interrupt a spell by running in circles, that won’t always work if you finish the cast too close to your initial location, aka corner casting. You would want to run in a straight line. Or duck.

I remember when Strut taught me I could escape pvp in Cobalt Scar on my cleric by casting Gate and clicking off levitate. The attackers would be unable to interrupt me, and the game will let you cast a spell through any amount of Z-axis displacement.