Hello, and welcome. I am a licensed attorney and happy to assist.
I'm sorry to hear of the situation and its effect on your health. Whether or not you may have a valid cause of action against the bank is dependent on the circumstances. You would definitely have recourse if the mold was known by the bank, but not disclosed and was something you would have no reason to discover through reasonable inspection at the time of purchase. The problem here is that you knew of the mold and discounted its importance, so the bank could not ordinarily be held liable for failure to disclose. An exception might lie if the bank knew it was toxic mold and misrepresented the situation as one involving a more harmless variety. In that case, the bank would be liable not just for remediation, but for damage to your health as well. It's a narrow exception, but worth mentioning.
I wish I could tell you the bank is strictly liable by the very existence of the mold, with nothing further, but having accurate information allows you to make informed decisions going forward.
I hope this helps. If you need additional information or clarification, please let me know and I will continue providing assistance. If I have addressed your concerns or pointed you in a positive direction, please remember to leave a positive rating when prompted, as that is how attorneys on this site are credited for the help we provide.
Good luck with this difficult situation.