One bad session doth not a burn-out make Oogar! Others have said that everyone gets bad sessions now and again. It can sometimes be worth going over, individually or as a group, to settle the reasons. But most times it's best just to shrug it off and move on.
If you really feel a little burned-out, then I suggest that first you look at the storyline you are running currently. More than once as DM I have begun an adventure that really fired me up, and then the actual experience turned out to be very disappointing. Sometimes it's just that your idea can't pan out properly, other times it's because the players just don't really like the idea. When that happens now, I talk it over withe the players, and if necessary the end of that storyline is simply described (as opposed to played out). The characters get a small reward for their players' understanding, and then we move on to fresh adventures. It's not worth slogging it out for an adventure that isn't working!
Still, good luck next session, Oogar. Don't let events demoralise you!