The Partridge Family star revealed he had been diagnosed with the memory loss condition last month (Feb17), blaming the health issue for a worrying concert performance days earlier, when he fell offstage in Agoura, California and forgot the lyrics to a number of his hit songs.
The news prompted an outpouring of support from fans online, while a number of famous friends also took the time to reach out to Cassidy - but messages from Connick, Jr. and U.S. broadcaster Katie Couric were the highlights of the bunch.
"I was particularly touched by the lovely personal notes from Harry Connick Jr. and Katie Couric, who are two of my favorite people," he told People.com.
The 66-year-old was also grateful for the positive vibes he received from his former TV co-star Danny Bonaduce, who has "reached out privately and publicly to offer kind words, encouragement and support.
"He's always been like my little brother," Cassidy smiled.
The veteran admits recent weeks have "been an amazing time filled with ups and downs," and while his ailment has forced him to retire from touring, he is not ready to quit music just yet.
Last week (08Mar17), he told fans via his website he is still planning to record a new album, adding, "I have my good days and very occasionally a bad day."