If there’s something literally (like, really literally) all people look for, it’s a great night’s sleep. Billions are spent on all things sleep, like sleeping pillows—something we know plenty about.

And here’s one of the plenty things we know—your pillow may be detrimental to your health. Let’s investigate why.

It’s not the right type for the kind of sleeper you are

Too soft, too firm, too high, too low—all of these variables and more interact with how you sleep (side, back, or stomach sleeper). If you get a wrong combination of variables, expect to feel like you’re waking up from the wrong side of the bed all the time. For example, if you’re a side sleeper with a low, flat pillow, your neck is going to take an awkward shape. You’ll be duly rewarded with a full day of neck aches as a result.

There are generally four ways to know what pillow is best for you, and it starts with what side you sleep on.

You’ve got a feather pillow

Feather fills, for as comfy as they initially are, aren’t really stable for the neck. It’s super comfy the first time you lay on it, but you start sinking. Then, you start moving in your sleep and it doesn’t adjust well to you when you move. This isn’t to say that a feather fill sleeping pillow or some other pillow with a fluffy fill isn’t for you. This is just to say that you might do better with something firmer, like a latex or memory foam sleeping pillow.

It’s cheap

If it’s a cheap $10 pillow that you’d find in a dingy motel, it won’t last long. A cheaper pillow might just wind up costing you more in the long run. You could be replacing a cheaper pillow sooner than the recommended 18 to 36 months, according to Sleep Doctor Michael Breus. If you invest more in a pillow, you can have a sleeping pillow that will maintain its structure and support for up to three years. This seems like a short shelf life, but think about the thousands of hours your beautiful brain container collapses onto your pillow. By year three, your pillow may be ready to give up the ghost.

In brief, know how you tend to sleep and after you do know, put good money into your pillow purchase. Do both well, and you’ll find your The One True Pillow.