You see, to Him, sickness occurs because of some very very fundamental things happening. e.g. "seeking outside yourself" produces sickness". e.g. "confusing the levels" (of consciousness) produces sickness. e.g. believing that causes are outside of you or that the body has its own will, produces sickness.
So really, when there is ANY seeking outside yourself, ANY reversal of cause and effect, ANY level confusion whatsoever, whatever results from that is given the label "sickness".
Sickness includes all physical sicknesses, diseases and death. But it also includes all mental illness, all fear, all upset emotions, all projections, all false beliefs, or mistaken sense of identity, all unawareness or unconsciousness, all behaviors inspired by the separate ego mind, etc... absolutely every activity or attitude of the separated self is sickness. Even the existence of the body itself is fundamentally a form of sickness, because the ego made it to enforce separation. Believing that you are not one with other people is sickness. Any form of separation is sickness.
So when Jesus refers to sickness in ACIM, he's referring to AAAAAAALLL of the forms and facets of 'a sick mind' in all the ways it manifests or distorts on every level in every way. Similarly, all of this entire motherload of 'states of being' that are not pure and holy, are sickness. And sickness also = fear, because "healing is essentially the release from fear". So sickness and fear are the same thing, and all distortions in the mind, and all ego in any way shape or form is sickness.
So when Jesus says you can perform miracles to 'heal the sick and raise the dead', he also really does mean the correction or undoing of the entire ego thought system, the entire ego 'world' of manifested interferences and distortions and unholiness.