The Baal Hatanya says: Michla d’mheimnusa, bread of faith is the first night, miIchla dasvasa bread of healing is the second night.
His son the Mittler Rebbe explained; that if the healing brings somebody to faith, that because he was healed he thanks Hashem for healing him, it shows that he was sick (in his belief of Hashem) …, if however the faith brings him to be healthy, then he was never sick to begin with!
(אג”ק כ”ק אדמו”ר חלק טו עמ’ כא, הגדה של פסח עם לקוטי טעמים ומנהגים)