It really depends if you have other symptoms except for eye crust. If you also feel other discomfort, you may have eye disease. You need to check with your doctor.
If you don't have other symptoms, it is normal and you are fine. Eye crust is academically called rheum. It is a thin watery mucus discharged by your eyes during sleep. It is also called sleepy, sleepers, eye crust, eye boogers. Most of it will be washed away when the person wake up.
When you are sleeping, your reason of feeling the crusty eyes may be the eyes infection. The coming invisible bacterium in your eyes may cause it. You could use some eye drops with anti-inflammation to make your eyes get moisture and comfortable. You should also have the good rest for the eyes. The warm compress is also a good way.
Well, generally speaking, it is a common eye condition, causing the eyelids to be swollen and scaly-appearing at the base of the eyelashes. And you should know that if scales become coarser, the surface of the eye becomes irritated and forms crusts. And then, this crust falls into your eye, you may feel like you have "something in your eye" and feel crusty in your eyes. And according to some experts, it can be Blepharitis, which can be annoying. So you just need to be more careful about it. Maybe some cold compresses can be effective.