I propose they keep sleep dart as it is for now, except for the wake animation where the player takes damage but can do no mitigation - wake should be instant once the time runs out or damage is taken, no long animation.
For nade, I propose “underhealth”. Red health is added to the targets’ health bars. This health absorbs healing. Something like 200 or 250 on each target. Supports can use their burst healing to eat through it and tanks like hog and mauga can use their self-heals to remove it. It will take away a chunk of their self-heal but they are not useless while naded.
This means that supports can still heal targets and the tanks that Ana oppresses can do something about it themselves, but it will still impact them, and if their abilities are not available when naded then they can Ana can still get the same value some of the time. It also makes it more of a skill for Ana to track CDs and use nade more skillfully than the current nade which she can throw just about any time at hog or mauga, except if there is a kiri.