If I choose to work in another field while on FMLA and/or short term disability, what can happen? Will I have to owe money to the state or get fired?

No one can answer your question with any degree of certainty without reviewing your contracts, agreements, and legal documents. However, the general rule is that an employee is either able to perform the essential functions of their job or they are not. In some situations where physical or mental conditions prevent working employees may recover short term disability benefits while they are on Family Medical Leave. Remember that FMLA leave is unpaid unless the employee has accrued benefits or unless some policy of insurance covers their inability to work. Collecting benefits from any source due to disability generally requires full disclosure. For example, if an employee is receiving insurance benefits and returns to work that employee would inform both the insurance carrier and the employer that they have returned to work and both would want to know how much income the employee is earning, having returned to some type of work. Failing to inform insurance carrriers while receiving benefits or informing an employer that an employee is taking FMLA leave while working elsewhere could be fraudulent. That could include charges of insurance fraud although you should pay an attorney to review all of your documentation before working or continuing to make claims. You listed harassment as the area of discrimination or hostile workplace but there were no facts indicating that you were harassed. Hostile workplaces or harassment can occur due to race, religion, sex, national origin, gender, sexual orientation, national origin and any one or more other protected classes of employees. Stressful or uncomfortable or uncivil supervisors are not necessarily harassing nor unlawful. Many employees work for unpleasant supervisors but that does not make those supervisors "hostile" or lawbreaking if they are not targeting you or others because of the protected class or classes to which you belong. Is your stress caused by something you cannot change or control. Is your supervisor targeting you because of your disability or regarding you as disabled or because of some other protected class you belong to? This should be flushed out with an employment lawyer. You definitely should consult with an employment lawyer to confirm that you are not yourself potentially in violation of benefit recovery laws. Stress by itself may or may not be a disability. It depends on its severity and how it was caused or its origination. Remember that workers compensation claims without physical injuries or unusual assaults are rarely compensable and those claims are very fact specific. If your claim does not qualify as work comp it might be covered under STD but that would not necessarily mean that it was caused by a hostile workplace or discriminatory. It also depends on whether the stress stems from general workplace stresses or unlawful discrimination targeting one or more protected classes of employees. Get a legal consultation from employment lawyers sooner than later. Good luck.