Sennheiser noise canceling over the ear headphones are comfortable enough to sleep in even if you’re a side sleeper
Hard disagree. If you accidentally cover the mic in the right way, you'll be greeted by a loud, high-pitch feedback noise that will violently wake you up.
I've had both H450 and HD458, had the same issue on both of them, though as you note only on one side. Apart from that and them repeating "connection lost" forever, they are great headphones.