Depends if you had this all your life or if it is a recent event that happened a few years ago.
Any problems with your peripheral vision should be checked out by your eye doctor.
There is an eye disease that can cause peripheral vision loss, it is called Glaucoma, it is about too much pressure in the eye that can damage the optic nerve. When the optic nerve has been damaged by glaucoma, a person can develop tunnel vision.
With open angle glaucoma, there is no symptoms, until vision has been lost. This is why people should have there eye pressure measured on a regular basis.
You may not have this disease, but you definitely need to see an eye doctor straight away, so they can check your field vision and your optic nerve as well as your eye pressure.
There may be something else causing this problem, only an eye doctor can say for sure.