If you are at fault for an accident, then your collision coverage (if you have coverage) pays for your vehicle, and your first party benefits (medical payments, etc) pay for your injuries. If you do not have medical payments, or if the amount exceeds the amount of coverage you have, your personal medical insurance is usually the next in line.
Uninsured and underinsured motorists coverage will pay compensatory damages which an insured (you) is legally entitled to recover FROM THE OWNER OR OPERATOR OF AN UNINSURED OR UNDER INSURED VEHICLE because of bodily injury sustained by an insured. This coverage is OBVIOUSLY not meant to pay you for injuries you sustain in an accident for which you are at fault, however, that doesn't mean there aren't some attorney's out there that wont try.
But if YOU hit another driver and the accident is your fault, or if you get hit by a falling tree, or run off the road are you totally uncovered for it from an auto insurance policy even with underinsured and uninsured motorist coverage?
Well these three instances are all different. The first mean's you're at fault. The purpose of the um/uim coverage is so that you're protected if you sustain injuries for which you are not at fault. In any case, you should be carrying adequate medical payment coverage on your automobile policy in case you are injured.
**Keep in mind, I am a Pennsylvania agent, and that laws may be different depending on the state you reside in**