There's no reason not to work out today. If the excuse you just fed your trainer sounded a little sorry to you, imagine how it sounds to him.
Clients cancel their appointments all the time for all sorts of ridiculous reasons.
Nutricise talked to some trainers and asked for the worst they've heard. Exercise should be even more of a priority if you're busy at work. It will give you a boost, clear your head and help you stay more productive. Try taking a workout break and then getting back down to business. You'll never make this excuse again.