Flashbacks are a very serious symptom. Only you know your own history and good sense would have guided you not to disclose all in a general inquiry. If your flashbacks come from any kind of Post Traumatic Stress Disorder type of reaction, or if you know or suspect that you are an assault survivor, then you should see a psychiatrist. The problem will interfere with your training, but more importantly, it will interfere with your life. There are many other symptoms besides flashbacks that you could develop. If the problem doesn't stop quickly on it's own, get help.