Is it permissible to link not waking up for Fajr prayer with an abundance of sins, or to assert that a specific medicine is the sole cure and only treatment for a particular illness?

There is no impediment for a Muslim to attribute his shortcomings in obedience to his abundance of sins, for sins are a cause of laziness in obedience. However, this is not an excuse; rather, he must repent and strive to maintain prayers on time and in congregation. There is also no impediment in saying "medication is the cause of healing" if the speaker intends that the medication is a means to healing. Nevertheless, it is more appropriate to attribute healing to Allah, such as saying: "Allah healed me through this medication," or "this medication heals by Allah's permission."