From the Catechism of the Catholic Church
- Qualifications for reception.
a) One who has not received the sacrament of Baptism cannot be validly confirmed;
moreover, for the Confirmation to be lawful and fruitful, the recipient must be in the
state of grace, and, if he has reached the use of reason, sufficiently instructed.45 An
implicit habitual intention suffices for adults. The sacrament revives when an obstacle
of serious sin impeding its effect is removed.
b) Those to be confirmed should first be properly instructed in the nature, dignity and
effects of this sacrament, and the dispositions necessary to receive it worthily.43 Those **
who due to age or lack of intelligence cannot remember or follow the instruction may
still be confirmed**. Heretics and schismatics may not be confirmed unless they have
abjured their errors and been reconciled to the Church.
The comments regarding those with memory retention difficulties as mentioned above may apply to illness as well. Could you explain your problem to your priest and ask his advice and whether a test is required.