The most common "bad case" scenario in North America is lyme disease. It's easy to treat if caught early, but is disabling in the late stages (possible outcome

The most common "bad case" scenario in North America is lyme disease. It's easy to treat if caught early, but is disabling in the late stages (possible outcomes include psychosis). I don't think it is common for it to get bad, but catching it at all is relatively common if you spend much time in nature around the northeast corridor.