Drowning is painless, but it is extremely uncomfortable
You know how holding your breath feels very weird but it doesn't hurt? Or when you accidentally breathe in water when you're in a pool, yet it doesn't hurt, just it's uncomfortable?
It's pretty much that, no pain but very uncomfortable
I have a former friend who almost drowned to death several times. I can tell you from what they told me about it, it's anything but painless. It's one of the worst ways to die imaginable because of the terror and pain you feel.