RihannaTiredMonday.jpgRihanna, 23, canceled a second show in Stockholm, Sweden, on Wednesday -- citing exhaustion.

This was her second this week; she canceled another show on Monday (right, after leaving her concert) and Tweeted a photo of herself on an IV. She canceled the Wednesday show just 40 minutes before it was about to begin, leaving 13,500 fans waiting.

Live Nation Sweden says her health is "really deteriorating."

Refunds will be offered to the audience. Right now, attempts are being made to reschedule the two shows.

Buzz is that the singer was trying to rally herself to perform, but could barely stand.