Jesus gave the disciples power for very specific reasons: Against unclean spirits, to cast them out. Against ALL manner of sickness and disease; to cure or heal.
Casting out implies that demons aren't supposed to oppress people, for God hates oppression, and no demon is above God's power.
To heal ALL manner of sickness and disease implies that no sickness, no disease, irrespective of its name, kind, duration is greater than the power of God. Every manner of them is subject to the power of God. And God wants you well. He gave you a body with its parts to function well, because it matters.
You can believe what Jesus says because He is the TRUTH. And use the power of God to do exactly what he says. For failure to use it according to aforementioned instructions will result in demonic oppression and bondage by all manner of sickness and disease, and you will also have to account for it.
Confession: I choose to use God's power against demons; casting them out at every corner that they encounter me, and I refuse to harbor any manner of sickness and disease, in obedience.