You listed yourself as a first dan, so I assume you have been training for at least a couple of years and the problem shouldn't be with body position or anything like that. You might want to consider some kind of strength training as you get older (if you are not already doing so) to help counter the effects of old to some extent. If your muscles are losing strength, it could be effecting your ability to balance.
Has your diet and/or sleep schedule been changed recently? When I started to work night shift and my eating schedule/diet changed I had problems at first when I trained. My body couldn't do what it normally could do because of the changes and I had to focus on improving what I was doing as well as develop a stricter schedule for food and sleep.
Something one of my college professors told me that I, and many older people, find to be true is, "If you don't use it, you lose it." What ever you do to help your balance, keep doing it consistantly and don't stop.