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.
To maximize the effectiveness of Modafinil and prevent your body from building a tolerance for the drug, you should take Modafinil at your prescribed dosage only one to three times a week. Under normal circumstances, patients will feel slight improvement after the first few doses, with the positive effects becoming more and more pronounced as the medication builds up in their body.