You need to be quite irresponsible and blindly take large doses for extended periods of time to achieve this though - and there's a significant margin between what's considered a "too high" level and what's actually known to be toxic. Do keep your levels in check (you don't need to see a doctor to do that), but there's no need to be overly scared.

You can very much overdose with melatonin as well, leading to your sleep schedule getting worse and worse the larger the dose. Ask me how I know before assuming my risk tolerance.