Hi Alan...I just love it when people say that they wake up at a certain time every night/morning...because it has great meaning in Traditional Chinese Medicine! A TCM practitioner always asks you if you wake up at a certain time in the night (it's best to sleep right through).
I checked the chart and 4am is when the Lungs are at their peak activity time. (TCM is thousands of years old...you can read more about it here: http://lieske.com/5e-intro.htm)
Do you smoke? Your Lungs have a message for you...do you know what it is? Emotionally, the Lungs represent....sadness, grief, anguish, melancholy. Does any of this fit with you?
I would suggest doing deep breathing exercises....or at the very least taking deep breaths out in the fresh air a few times a day. Remember to fill your diaphragm...don't breath up into your head - don't elongate....expand width-ways....then let the air out. This will strengthen your lungs and perhaps help any lung issue you may have...relieve some stress etc...