Speed problems with my horse?

So I own a 13 year old Appendix Quarter Horse gelding. At the end of April he was ruuning 16.3's in barrel racing at an arena. A huge wave of EHV-1 hit our area, so I was out of competing for about a month. And while I was out of competing, I did practice with him on barrels, poles, etc. Now there's a summer series of speed at the same arena we were running 16.2 and 16.3's at. Now he's running 17.0's and 17.5's there. The first Summer Series, he ran a 25.4 in poles, a 17.5 in barrels and a 10.4 in straitaways. Before he was running 23.1's in poles, 16.2's in barrels, and 9.8's in straits. I went and ran him again today, we got a 17.0 in barrels and 10.4 again in straits. What's wrong? It's like all of my horse's speed has dissapeared! Pleas help! Thanks so much!