dnd 5e – Is the act of suffocating considered to be taking damage?


Is it considered that the act of suffocating is taking damage?

Example:

A green witch is poisoned with the poison of Taggit oil and falls unconscious. Then it is carefully placed in a portable hole and then the hole is closed.

After 10 minutes, the witch must be out of the air due to the properties of the portable hole. At that time, she would be suffocated, but would not receive any "damage" until after her third turn (she has a mod of Con of +3). At the beginning of her fourth shift in the portable hole, she would immediately fall to 0 hit points and would be dying.

Will the effect of the poison disappear immediately as soon as it begins to suffocate? Or would he remain unconscious until he began to die?