"Is any among you sick? Let him call for the priests of the church, and let them pray over him, anointing him with oil in the name of the Lord."
Sacrosanctum Concilium, Vatican II Constitution, emphasizes: "[anointing of the sick] is not a sacrament for those only who are at the point of death. Hence, as soon as any one of the faithful begins to be in danger of death from sickness or old age, the fitting time for him to receive this sacrament has certainly already arrived" (SC 73).
Yet, this sacrament is not for any type of illness or condition. The Instruction for the Rite of Anointing states:
"great care and concern should be taken to see that those of the faithful whose health is seriously impaired by sickness or old age receive this sacrament" (§8)
"the sacrament may be repeated if the sick person recovers after being anointed and then again falls ill or if during the same illness the person's condition becomes more serious" (§9)
"a sick person may be anointed before surgery whenever a serious illness is the reason for the surgery" (§10)
"sick children are to be anointed if they have sufficient use of reason" (§12)
this sacrament "is not to be conferred on anyone who remains obdurately in open and serious sin" (§15)
it is not for those who "are ill or have reached an advanced age...only those whose health is seriously impaired by a sickness or old age are proper subjects for the sacrament" (§108)
As such, this sacrament is reserved for those in danger, even beginning to be in danger, of death from a malady or from old age. It is not for those who, for example, have: most mental conditions, stress, headaches, arthritis, allergies, physical debilities/injuries, flu/fever, or even for some cancer patients, provided that the individual at the moment has not started to be in danger of death. It is the sacrament which prepares the soul for the proximity of death.