If you're in decent shape and as Jerry said, you aren't light-headed when you stand, 53-59 bpm is good. My resting HR is usually between 55-65, sometimes as low as 52-53. I'm not fantastically fit, but have been in a physically demanding job for the majority of my adult life.
I think I got some good genes from my father as well, who used to run marathons and had a resting HR in the low 40's.
I also saw a doctor on this site somewhere tell someone else not to get caught up in specific definitions (like of bradycardia), because everyone is different. That your heart rate is below 60bpm may simply mean you have a resting heart rate below 60, and nothing else. If you're in good health, enjoy it!
I think that T.M.T. may be short for Tread Mill Test...Just my thought:)
A rest HR of 53-59 is fine, even great if you feel good. That is when you stand you are not dizzy or light headed. That low a rate is most often seen in people who are in good shape and active athletes. I suppose there are some who are born with an unusually strong cardiovascular and have that resting HR without having to "work" for it.
The simplest test is to have an experienced doctor listen to you heart with a stethoscope, and if they agree, or if they consider it part of a physical exam (in the US I think it isn't normally done in an annual physical exam before the age of 40) get an electro cardiogram (EKG, or ECG normal abbreviations). If that all looks good it is unlikely that a doctor would prescribe further tests, but the next in my mind is a stress test (on a tread mill) and if that discloses any questions it may lead to a nuclear stress test. The next (may be I'm working my way up the cost ladder) would be an echocardiogram, which is the "gold test" for the physical condition of a heart, including valves and efficiency.
Hope that helps, I do not know what a T.M.T test is.