Is the Otovent Safe to Use?

Yesterday I tried to use the Otovent for the first time. I tried inflating the balloon with my nose, but it was way too stiff. So I searched for guides on using the Otovent and found this video:

How to use the Otovent

The ENT in the video recommended inflating the balloon with your mouth first then putting it up to your nose, so I tried it this way. The balloon was very hard to inflate with my mouth (first clue that I should have picked up on), but I managed to inflate it. I then put it up to my nose and plugged the other nostril. When I opened the balloon and swallowed I felt a pressure in my left ear greater than anything I've ever felt in my life. No pain but it was an uncomfortable feeling to say the least. I felt a little light headed for a few minutes afterwards.

It's been a day and so far there's no increase in tinnitus or decrease in hearing, but definitely won't be doing that again.