Is the act of suffocating itself considered to be taking damage?

Question

Is the act of suffocating itself considered to be taking damage?

Example:

A Green Hag is poisoned with the Oil of Taggit poison and falls unconscious. She is then carefully placed into a Portable Hole and then the hole is closed.

After 10 minutes, the Hag should be out of air due to the properties of the Portable Hole. At that point she would be suffocating, but not taking any “damage” until after her third turn (she has a Con mod of +3). At the start of her 4th turn in the Portable Hole, she would immediately drop to 0 hit points and be dying.

Would the poison's effect immediately wear off as soon as she starts suffocating? Or would she stay unconscious until she started dying?

Answer 1

The rules for suffocation are:

A creature can hold its breath for a number of minutes equal to 1 + its Constitution modifier (minimum of 30 seconds).

When a creature runs out of breath or is choking, it can survive for a number of rounds equal to its Constitution modifier (minimum of 1 round). At the start of its next turn, it drops to 0 Hit Points and is dying, and it can’t regain Hit Points or be stabilized until it can breathe again.

The hag will have 10 minutes of air as per the description for the Portable Hole. It will then be able to hold its breath for 4 minutes before it begins to suffocate. After a further 3 rounds it will drop to 0 hp - this is when it takes damage and the unconsciousness from the Oil of Taggit will end, however, the hag is now either dead (which is the default for a monster reduced to 0 hp) or unconscious and dying from the effect of Suffocation (if the DM decides that this particular monster doesn't die at 0 hp).