Justin Bieber's whirlwind lifestyle may finally be starting to take a toll on him, as the singer recently had to withdraw from his scheduled performance at the Macy's Thanksgiving Day Parade.

TMZ reports Bieber abruptly pulled out of producing the taped performance for the parade, as well as a scheduled Tuesday night live appearance on "The Late Show with Stephen Colbert."

Word is the 21-year-old Bieber is "totally spent," both physically and emotionally, and plans to use his remaining energy to promote his soon-to-be-released "Purpose" album.

Sources add Bieber has recently been on an emotional roller coaster, with his moods often swinging back and forth as he deals with an assortment of "personal issues."

Among major recent changes for the pop star are his apparent reunion with on-again, off-again girlfriend Selena Gomez. The two have recently been seen out and about together including in Los Angeles, where Bieber was spotted serenading her at the Montage Beverly Hills.

They were also seen hanging out together at Bieber's American Music Awards after party, also in Los Angeles, late Sunday night. They are reported to be spending more and more intimate time together.

"They both have an understanding that how they are playing things now is the exact route things should progress for the time being," a source told Hollywood Life. "They are going to hang out, and have their meet-ups, but they will not endure the media circus they would get into if they went exclusive again with each other. Selena wants more, but is accepting the way things are going because it allows her to still be in Justin's life."

At the AMA after party bash, the two were part of a crowd that feasted on cake in celebration of Bieber's red-hot album. A source added Bieber also regaled the crowd with a piano rendition of the Beatles' "Let it Be."