Is ADHD a phase?

[CaroleD]

My 15 month old has been a retrieving machine for several months now. He can be somewhat ball-possesive, but it's not been a huge problem. The fetch play has been great because we have a large fenced-in yard, and I am in the habit of taking him outside for 20 minutes or so a few times a day (during the day) to burn off excess energy by ball chasing. This allows me to give him exercise even if I'm dressed and clean (walks are still a perspiration event here in the south).
Lately, Dylan acts all excited about chasing the ball, but he'll retrieve a couple of times and then will become distracted by snuffling in the bushes, wandering around or smelling stuff on the ground. He will return to me if I call him, but without a lot of enthusiasm. This distraction seems to happen only during the afternoon hours. Later in the evening, he is much more focused -- even retrieving in the dark (we have a glow-in-the-dark ball).
Does anyone have a similar experience? Please tell me it is a phase.