State law governs workers' compensation systems, and thus what injuries are covered by workers' compensation differs from state to state. But generally, an injury that arises "out of the course of employment" will be covered under your state's workers' compensation system. This means that injuries that happened while you were performing your job duties, or diseases/illnesses arises from conditions at your job, will likely amount to a workers' compensation claim.
If you are injured at work, and the contents of a first-aid kit completely remedy your injury, the injury is not severe enough to warrant a workers' compensation claim. Cuts, scrapes, small wounds, or even a single headache are insufficient. If, on the other hand, you are exposed to a chemical that causes routine headaches, this is an occupational disease that amounts to a workers' compensation claim.
Injuries suffered outside of your usual office or building where you work may still be workers' compensation claims. If you were acting in the "course and scope" of your employment, meaning you were acting within your job duties, carrying out the business you are required to do, you are covered under your state's workers' compensation system when you are injured. For example, if you are driving to visit a customer and are involved in a motor vehicle accident, with injuries requiring more than simple first aid, you have a workers' compensation claim. Generally speaking, if you are getting paid for doing what you are doing, and are injured while doing it, you likely have a workers' compensation claim.
Commuting is not considered in the course of your employment. Therefore, injuries suffered while commuting, with rare exceptions, do not give rise to a workers' compensation claim.
Similarly, when you are out for lunch, you are outside the scope of the workers' compensation system. Horseplay and fighting also do not fall within the scope of your employment, or injuries caused by alcohol or drug use, so injuries sustained during these activities generally are not workers' compensation claims.
There are many conditions and diseases that can give rise to a worker's compensation claim besides one-time accidents and injuries. Conditions such as carpal tunnel syndrome or respiratory conditions from repeated chemical exposure are frequent workers' compensation claims. These conditions arise over time due to repeated events at work. In many states, these types of conditions and diseases are called "occupational diseases," meaning they are a condition that arose from the conditions of employment over a period of time. In other states, they might be referred to as cumulative trauma injuries or repetitive stress injuries or simply slowly developing injuries.
If you question whether your condition may be due to your activities at work, talk to your doctor about your concerns. Your doctor will be able to assist you in evaluating potential causes of your condition or disease, and help you file a worker's comp claim if he or she determines your work may be the cause of your condition/disease.
Mental health conditions can be workers' compensation injuries or occupational diseases, too, just like physical conditions. Most states cover both psychiatric injuries from singular events, such as post-traumatic stress disorder (PTSD), and conditions arising over time, such as depression and severe anxiety.
Many states have regulations regarding stress as a compensable workers' compensation claim. Most people experience stress in the workplace to some extent, so you may not have a workers' compensation claim due solely to work-related stress. If you believe you have a stress-related workplace injury or condition, talk to your doctor and possibly a lawyer about filing a claim.