Your Sensei has probably already noticed the "shift" in you. The best thing you can do is be honest with yourself and the dojo. If you have lost your enthusiasm then stop training and see what happens to you. If nothing then it will be of no concern to you. However, if you notice that something is missing, an outlet for you to work through your issues perhaps, or just a general feeling that something is not there anymore then go back and rediscover Aikido with your new eyes. The worst thing is just to go every now and again.