I have very bad teeth. a lot of my back teeth are broken off. i have a metallic taste in my mouth. i also spit up a brown substance & a little blood.

Gum disease: You likely have bad teeth due to poor dental hygiene with gingivitis the complication. This in turn causes you to lose your teeth and the minute bleeding from chronic gingivitis causes the discolored discharge and the metallic taste. Since chronic inflammation from gingivitis is unhealthy, need to see dentist ASAP. He will also likely provide you with info to keep your teeth healthy in the future

Dental Visit: There is no doubt you are way overdue for a dental evaluation. Please see a dentist. It is unknown if the brown substance is related to your oral health.

Assume: I assume you're asking is this, OK, serious, and what can be done about your many symptoms. Yes, it's serious. Probably both infected teeth and infected gums. If you had an infection anywhere else in your body would you ignore it? You know what you have to do...call a Dentist. Do what you need to do to become healthy again. Don't wait for your chronic problem to become acute.