Hi Naveeda and welcome!
I used to face the same problem and I realised that this happened whenever I was not well prepared for the lesson (maybe because I felt rather too confident...!).So I started preparing very carefully the following day's lesson and that helped me a lot.That meant, of course, lesson planning. In my humble opinion, defining the objectives of a particular lesson and checking your knowledge before going into the class are the most important factors. Don't get disappointed. We've all gone through situations like this.