Most tenant's rights are protected and enforced by written documents. If your lease is in writing, look for sections providing for "conditions". The problem should be memorialized in a letter to both renter and apartment owners that sets out the problem and what you want to have done about it.
If there is not a violation of the village ordinance then there's not much local officials can do about it.
The concept in the law is the right of "quiet enjoyment" Legal action may be tricky and difficult but if the problem has gone on so long, the only avenue may be to take it to court for damage (the effect of the loss of sleep) or injunction against the downstairs neighbor.
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Unfortunately, Oak Park does not appear to have a "landlord-tenant" ordinance that defines what might be a breach of landlord obligations or what a tenant's rights might be.
Under general landlord-tenant law, your lease is the primary document that would define what your rights are. Unfortunately most leases only tell you as a tenant what you can and can not do, and do not particularize the landlord obligations.
However, if things changed as you say, during the term of your lease, and have made things so bad that it has made your apartment "virtually" uninhabitable and the landlord refuses to address the situation in a reasonable fashion, you MAY have the right to declare a "constructive eviction" and move out but I caution you not to taken any steps in that direction (a) if you prefer staying and (b) before consulting with an attorney who can guide you through the process if after a full consultation and full review of your lease that is your only available option. A fair amount of documentation would have to be assembled to prove your case.
If you prefer staying, yes you would have to sue, but the question is, what are your damages? The right to enjoy your apartment in relative peace and quiet is usually an implied lease term, but quantifying it in dollars is what may be be difficult (you say it has affected your health and medical bills are quantifiable but that means you would have to be out of pocket for those fees and any medications associated with dealing with the situation) and in the end is it only dollars you seek, or the peace and quiet you deserve?
Sometimes the threat of losing a tenant is more potent.
You need to stay on it with your local police department. Most have some sort of mediation program between neighbors. If they do not then you must ask that they be ticketed for an ordinance violation. If they get enough violations they will eventually get the message. Bring witnesses with you to court. You may want to contact a local attorney to handle this.
IF YOU FOUND THIS ANSWER HELPFUL PLEASE MARK IT SO. This information is provided by PEGGY M. RADDATZ, Attorney At Law as a pro bono service. YOU SHOULD CONSULT WITH AN ATTORNEY IN PERSON who has specific expertise in the area of law you are asking about.