Tylenol is interesting - it's a psychoactive drug. It reduces your brain's ability to experience pain, or even understand the possibility of pain, rather than reducing the amount of pain you're feeling. That means different people's brain chemistry will result in very different results with Tylenol.
Studies were done that show people are slightly more likely to take risks when they're on Tylenol. Wild stuff.
An "instance" is a server that talks to all the other Lemmy servers, where your account info and login are stored. There's a lot of benefits to decentralization - even if one instance goes down, like lemm.ee, it doesn't really impact the whole of Lemmy too severely. The cost of running an instance isn't super high, which means that if an instance is being annoying about advertising or something, you can ditch it with little cost to yourself and even run your own instance if you want. A single cabal of admins can't ruin it like Reddit (cough cough Spez) and it can be easier to curate your own experience by choosing what instances you want to ignore completely.
Any given instance is not necessarily a safe harbor, but as long as Lemmy is around, there will probably be multiple instances to choose from. The only thing you really lose is your post history - and you can link to your old account info in your new account for continuity's sake.