Does my situation count as سلس ( سلس in this context refers to سلس البول or سلس الريح, commonly translated as incontinence or involuntary discharge, but for religious rulings, it's specific to ritual purity and prayer, often meaning a continuous or near-continuous state of discharge that makes it difficult to maintain wudu'), and what should I do if a lot of wind is discharged from me during prayer due to a stomach illness, given that I am unable to distinguish beforehand whether it will be continuous or not, and is it permissible to resist (the urge to pass wind) even if it causes severe pain?

It is not obligatory to hold back gas, and it is disliked to enter into prayer while suppressing it. The prayer of someone who is suppressing the urge to defecate (haqib) or urinate (haqin) is disliked, even if this condition arises during the prayer. The impermissibility of holding it back is further emphasized if doing so causes harm. A person who suffers from uncontrollable flatulence is subject to the ruling of one with chronic discharge (sahib al-salas); thus, she should perform ablution after the time for prayer begins and pray with that ablution, and her prayer will be valid, with no need for repetition. It is preferable for her not to lead others in prayer unless their condition is similar to hers.