Most of us have no problem calling in sick for work when we have physical symptoms - really bad cold or the flu for example. However, a lot more people worry about taking a mental health day. The truth is, when you call in sick, you aren't really required to disclose what the illness is, and your mental health is as good a reason to call in sick (if not better, because burnout can also make you more prone to getting physical illnesses due to a weakened immune response). While a lot more companies are promoting mental health and encouraging employees to take mental health days, sometimes it can be a bit hard to tell when you actually need one. So, here are a few things to watch out for, that could be signs you just need to "take the day."
Your Mood Has Changed - this might be feelings of sadness/depression. Feeling anxious about work (or other things in your life). Angering or feeling frustrated easily. This is especially tell-tale if you're normally happy or "perky" at work or if there is no other explanation for these changes. And even if there is an explanation, it might be good to take a day off anyway (maybe schedule a therapy appointment or some other form of active self-care like yoga)
The Quality of Your Work Has Decreased - This may come in the form of an actual performance review, but typically we are aware of how "good" our work is long before it comes to review time. If you've noticed it's slipped or you just don't care as much about it, you may be feeling stress and/or burnout. A mental health day won't necessarily fix burnout but it can help with stress (again, if you use it productively).
You Dread Going to Work - If you like your job and normally enjoy going, and today it seems like the worst thing in the world (especially if you've had a few of these days recently) might mean it's time to take a day off to regroup and connect with your values around work and why what you do is important to you.
There are of course a lot of other signs that it might be time to take a day off. These are some that are often overlooked. Remember to always seek help from a licensed mental health professional in your area if you need it.