This topic seems to be coming up a bit in the main groups so I thought I might touch on it here lightly if I could:
Firstly what its important to understand is that the body and mind (and soul) are one functioning unit. So, if one part of the equation is not functioning correctly, then neither is the other. This gives us great opportunity to see into the mechanism behind depression and not only use the body to diagnose it, but also to cure it.
Secondly, many here are also meditating daily (if not all of you) and this can, in certain stages bring up periods of depression. It is important to distinguish between the source of the depression - that which is caused by meditation and energy transformation, that which originates organically from the body and that which has its origins in the mind (which can overlap somewhat with both of the other two).
Depression which is purely physical in nature often corresponds to a lack of bioelectricity - this is the most common form and will manifest as anxiety or sadness - long term grief can also cause the physical symptoms.
Some common patterns of this include Lung Qi Deficiency which manifests with a cough that is worse after exertion, fatigue, shortness of breath, spontaneous sweating (sweating for no reason) and inhalation which is longer than expiration (breathing in feels easier than breathing out).
Another, more chronic pattern is Kidney Yang Deficiency which might manifest as feeling cold, lower back pain, frequent pale urination or the feeling of needing to go to the toilet even after having already been, early morning (4-5am) diarrhea with undigested food in it, loss or significant reduction in libido and fatigue.
Other syndromes which are similar will share some of the above symptoms along with abdominal bloating, poor appetite, loose stools (diarrhea) and possibly organ prolapse in advanced and chronic cases.
There are very effective treatments in the way of herbs for this and which herbs are for you depends on which syndrome you are presenting with.
Another manner by which depression can occur is through obstructed or improper flow of energy around the body. This tends to originate in the mind but can also have physical precursors. The typical presentations are as follows:
Liver Qi Stagnation - Irritability, feeling of something 'stuck' under the ribs, frequent sighing, abdominal pain, shoulder or hip pain, cold hands whilst the remainder of the body stays warm, headaches around the back of the neck and head area and alternating constipation and diarrhea are the principal manifestations here.
Dampness of any etiology/location - the symptoms vary depending on where the dampness is obstructing but it may present with numbness of the extremities, early morning headaches in the front of the head and behind the nose, sinus congestion with copious phlegm expectoration (may also be coughed up even in the absence of an infectious illness), often there is a tendency towards weight gain or fat deposits, there may be a heavy feeling or mental 'fogginess' which obstructs the concentration and there may be dark yellow urination or frequent pale urination.
Again these syndromes can very easily be treated. Note that there may be significant overlap betwene one or more of the above syndromes, additional physical signs (or less) and other factors (medications etc which obscure symptoms and the like).
I will touch on the meditation/soul related depression in another post, as I am low on time currently..