Last night i was playing with marley and the lazer light. i noticed he was getting a little over exherted when he started panting really heavy. then he started coughing, nothing came up. He continued panting for about a minute, not much longer then he was fine. why would he do this? i was in the bathroom and could hear him breathing from down the hall. he has done this once before when we played with the lazer light, then he was fine just like last night...any thoughts??