I had a similar experience on an Alaska Airlines flight from Anchorage to Seattle, immediately after takeoff and at about my guess around 10k level my ears started popping suddenly and their was a bitter sharp smell in the cabin, my guess is the cabin presurization valves went off kilter or vented suddenly, plane did a deep descent and you could actually feel the pressure building up. Landed and changed planes.
Crew and passengers would be fine up to around 14,000 feet MSL. Above that, expect a little shortness of breath. Above 18,000 feet pressure altitude hypoxia starts setting in, depending on one’s aerobic condition.
And yes, the crew used poor judgement saying the words “going down.”
TC