Most of the time we never realize the exact cause for being sick or have immunity low, the answer is energy within you,
as per Bhagwad Gita we all are form of imperishable energy, :
"na jayate mriyate va kadacin,nayam bhutva bhavita va na bhuyah,ajo nityah sasvato ’yam purano,na hanyate hanyamane sarire" (Bhagwat Gita: Chapter Two verse 20)
"The soul is never born nor dies at any time. Soul has not come into being, does not come into being, and will not come into being. Soul is unborn, eternal, ever-existing and primeval. Soul is not slain when the body is slain."
This energy within us have various forms, it is in form of karma, words, thoughts, and actions we perform, not just physical body,
The most beautiful form of energy in us is our thoughts, because thoughts manifest our words and actions, now let us assume you are sad or depressed due to some reason, now the energy of being sad or depressed is within you, and it flows all across your body from top to toe and vice-verse,
This same energy is like dormant volcano within you, somewhere or other it will get stuck if not released and when this energy is stuck at certain point in body, the pain or ailments starts, we get sick or have unwanted pain as guest within us,
The energy requires channel to vent out in order to not to have any stagnant energy within you, because stagnation of flow of energy will be like still water, either it will become stale or evaporate, which likely to happen with us,
Every emotion or thought is powerful energy, we should always realize, we are made of atoms or atomic bombs, there are billions of these bombs within us, we need to channel this atomic energy created by our thoughts, words and actions,
How we release the energy of thoughts to avoid being sick or before we become active volcano of ailments or pain within us,
Simple is, share with someone your feelings, thoughts or emotions, someone who can listen to you with all the love and care, once that energy is released, you will be more synced and streamlined in your thought process and actions and words,
You just need to vent out and share from time to time to known or unknown source, be it God, nature (hugging tree or walking bare feet), idol or close friend, just release your thoughts, don't create a prison for them and the energy these thoughts are creating within you, which at the end of the day will erupt on physical body and cause major damage,
The manifestation of energy within us can be synced by various Vedic Mantras and Shlokas, if chanted regularly and so do the ailments can be helped, write to know more.
You can share your thoughts or feelings likewise at https://www.spiritualveda.org/aum-meditation
Always remember, you are not alone, be reached or reach out, holding energy can be damaging for self and others around,