Yes, it's because you're not a doctor. Reflexes won't simply vanish. The only reflexes I can trigger on my own are the knee ones, and I have over-reactive reflexes (I've nearly booted some doctors in the face ;) ) so you'd think I'd be able to find them! But no, you don't need to be worried. I'm pretty sure it's normal to not be able to trigger your own reflexes, like tickling yourself, especially when you're not trained on how to find them.