The most common though that I see in BJJ is the cervical sprain or strain. The cervical spine is the most mobile segment of the spine however it puts it at a high risk of injury. Cervical sprains/strains are soft tissue injuries. A strain is linked to muscle, while a sprain is linked to tendons.
However, for some people, effects are much shorter and they have to take modafinil 2X per day (albeit this is not that common). For other people, effects can last 20-24 hours. It all depends on how your body processes it.
One 2-300mg dose and some caffeine keep me in good shape for maybe 10 hours, after that I can go another 6-8 or so before I'm borderline zombie mode. If I wake up at 7am Friday, I could take one dose of modafinil around 10pm Friday evening, and I would not need more modafinil until around 9-11am.