I am a 55 year young African-American female who, for at least the past 6 years, has been very active(walk at least a couple miles a day in addition to working out with weights and aerobic exercise). I have very healthy eating habits consuming mostly fruits, vegetables, nuts and seeds and plenty of water (1/2 gal. or more a day). For the past 2-3 months I feel a tightening in my diaphragm area while walking, usually uphill, upstairs or any type of incline. I have no shortness of breath but often feel like I may pass-out from being lightheaded. Whether I stop to rest or not the sensation passes within a minute or so. I was wondering if this might be symptoms of some vitamin deficiency.