"if you're unfit" is not about one person in one instance. It's stating a general condition; when the condition exists where people are unfit, these people have an excellent chance of hurting themselves. The present simple form is usually used to describe this general condition.
Also, I'll suggest that there is a semantic difference at play here. For this situation, 'will' does not equate to "a huge chance". That would be described by "very likely will".