To heal an occult illness, we use several spiritual and material means, as cited by Imam Ibn al-Qayyim.
On the spiritual level, we use ruqyah, which we can perform ourselves, with supplications and invocations.
On the material level, Zamzam water, preferably recited over with Qur'an, will be very beneficial, whether used externally or internally. Oils recited over with Qur'an are also helpful for massages, particularly on the affected areas, as with Hidradenitis Suppurativa (Verneuil's disease), for example. Furthermore, "the seven prophetic remedies" have proven effective in treating cases of ingested sorcery in particular. Indeed, people who have consumed them have been able to heal, seeing their anxieties, psychological problems, and even depression disappear, when combined with night prayers, charity, and supplications.