A lot of people have commented on how the Undertaker looked old and haggard at Summerslam. He did look a little beaten up and I think he even coughed when he cornered Rey and started speaking to him.
I think this was all done on purpose by the WWE. The WWE is very protective of the Undertaker character and they would never let him look like that unless it was for a greater reason. Going forward, this whole angle is going to be about Undertaker losing his powers after Kane beat his older brother into a “comatose state.” Kane got the better of Undertaker at Summerslam, which is a great indication that the WWE wants Kane to look like a monster right now while Taker is the underdog who has lost a little something.
I wouldn’t be shocked if the urn and Paul Bearer make an appearance in this feud to help Undertaker rekindle his powers. It’s more wishful thinking on my part, but you never know.