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.
They started me out at 100mg and raised it to 200mg after 2 weeks. The 100mg dose helped but 200mg made all the difference. 200mg seems to be the most effective, especially for long term use. One of the things I really like about Modafinil is its subtlety.