All condominium developments - and apartments - have an association who needs to be notified of such a problem - immediately. They usually have their own companies for such work, so, don't spend money getting your own inspector or workers, when the association might not reimburse you for those costs.
To add insult to injury they might even rip out work that you contracted for, to redo with their own people.
Call the association - immediately. Good luck in solving your situation.
Ohhhh mold is not good! Hopefully it's not toxic, but you need to get an inspection right away to find out. They will take samples. If this is caused by the upstairs condo, they are responsible to make the repair. Mold remediation can be very expensive, so don't let this go much longer...not to mention the toll it can take on your health.
Good luck...I would call suggest that you use Jack Clausen at http://www.jlcinspections.com he is a mold expert and reasonable for inspections.