Hello, sir, you are feeling gas in stomach along with general fatigue,
dizziness, and breathing difficulty during your long distance walking, I want to know about your age group, if you are above 40, than once you consider cardiac checkup and blood pressure monitoring, also go for TMT once, so any worst can be ruled out.If you feel better without any
vertigo ,or extreme feeling of weakness, than once you can think of APD(
acid peptic disease), which may be due to
anxiety or late night waking up.So here is my suggestions for you to take simple fried free food and avoid late night waking up , also try to remove your anxiety if any along with some medications like Rabiprazole with
domperidone daily with anxiolytic such as alprazolam 0.25 once in night and start walking in morning if possible along with fat free, low salt diet. Hoping you will like my suggestions , good luck take care.