Can I send the request for the visa extension via post? 

You can send filled request for visa extension – at the latest on the last day of your legal stay in Poland, although the current photography and all the documents, which confirms circumstances enumerated in your request, as well as the confirmation of the possession of the financial means of support and the health insurance, you are going to need to submit in person in the office – in another case the proceeding will not begin. The exception of this rule is the situation when you currently stay at the hospital.