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.
Although modafinil has been around for over 20 years, experts are not sure how long-term use affects the brain. Some are concerned about chronic sleep deprivation, future ability to sleep, increased antisocial tendencies and a suppressing of emotions, as well as problems coming off the drug.