Medicare is an important program that gives millions of seniors access to essential health coverage. And as an enrollee, it's important that you try to take advantage of the benefits under Medicare you're entitled to.

But failing to understand Medicare's rules could put you at risk of forgoing coverage you're eligible for. In a recent MedicareAdvantage.com survey, enrollees of the program revealed that lack awareness in the context of certain elements of their Medicare coverage. But here are four essential benefits you don't want to miss out on.

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1. An annual wellness visit

Medicare enrollees are entitled to a free wellness visit once a year. Attending this appointment could be a crucial part of maintaining your health, as a doctor can check for hidden problems and identify issues early on. And nipping health problems in the bud is often less complicated and expensive than treating problems that are left to escalate.

In the survey, though, only about 73% of respondents knew they were entitled to a free wellness visit through Medicare. If you haven't scheduled yours yet, you may want to get moving.

2. A yearly flu shot

The flu vaccine won't necessarily prevent the virus itself, but it might lessen the severity of its symptoms. Medicare will cover the cost of a flu shot every season. Yet only about 64% of respondents were aware of that in the survey. If you haven't gotten your flu shot yet this fall, you may want to hurry before flu cases start to explode.

3. A walker or wheelchair

Some seniors end up struggling with mobility due to aging or injury. In the survey, only about 29% of Medicare enrollees knew that the program would cover the cost of durable medical equipment like walkers and wheelchairs.

This doesn't mean you won't have to pay anything out of pocket. But Medicare will generally pick up the bulk of the tab if a medical professional indicates that you have a need for a wheelchair or walker.

4. Inpatient or outpatient mental health treatment

Mental health problems can, in many cases, be just as serious as physical health issues. And these problems can also creep up during retirement as seniors struggle to make the transition from maintaining careers to having more time on their hands.

Medicare will cover a variety of mental health treatments that extend to both inpatient and outpatient services. In the survey, only about 29% of respondents were aware of that fact.

It pays to read up on Medicare

Whether you're new to Medicare or have been receiving health benefits through the program for years, it's important to read up on the coverage you're entitled to. There are actually a host of free services Medicare will pay for, including certain diagnostic tests, and you don't want to forgo that care if it may be beneficial to you.

So take the time to learn more about Medicare. And while you're at it, take the time to explore your options for coverage during annual open enrollment, which is happening right now through Dec. 7.