Is it actually healthy for me to take 5mg of melatonin?

1 mg or less : Higher doses of melatonin can actually interfere with normal sleep. Take 0.3 to 1 mg. And see how you do.

Melatonin: Patients with insomnia related to psychiatric conditions often require 5mg of melatonin (and off label higher doses are also used). One should address cause of insomnia first. Sleep hygiene is also very important. Discuss use of any supplement or herbal with your physician - especially if you are taking medications.