Is it okay to use a sports mouthguard than a sleep mouthguard for sleeping?

Sure, but . . .: You can use a sports mouthguard for bruxism (grinding your teeth at night), and will protect your teeth from damage as a sleep one would. But neither one will actually treat the reasons for the grinding of your teeth. A hard mouthguard, and/or medications, plus relaxation therapies are more geared to preventing the grinding; discuss it with your dentist, or one familiar with tmd treatment.