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.
If you are using modafinil for shift work sleep disorder, take it by mouth with or without food as directed by your doctor, usually once a day 1 hour before you start your work shift. The dosage is based on your medical condition and response to treatment. Take this medication regularly to get the most benefit from it.