Zayn Malik is hitting pause on his big comeback because his health just took center stage. Sources familiar with the situation confirm to TMZ ... the singer has canceled his planned appearance on "The Tonight Show Starring Jimmy Fallon " set for Tuesday to promote his new album "Konnakol" ... after a scary hospitalization. Zayn himself broke the news Friday, posting a photo from a hospital bed and telling fans he was "unexpectedly recovering" after a "long week." He didn't reveal what landed