No, that is not willful misconduct. It is not an intentional violation of the Employer's interests to have health problems. Now if your health problem was very slight, that might give an unemployment referee pause. More facts are necessary.
Your employer has the right to discharge you for violation of its attendance policy. it is very difficult for employers to prove that poor attendance rises to the level of wilful misconduct. if your employer is challenging your entitlent and a hearing has been scheduled, hiring a lawyer would be a good idea.
This answer to your legal inquiry is based upon the limited facts stated in your question. Accurate legal advice is based upon an exchange between a lawyer and a client. The lawyer can then ask about other facts that may change or confirm the answer. Without that exchange, this reply should be considered limited in value. You should rely on this answer only at your own risk. Direct consultation with a lawyer is always recommended. Answering your question does not create an attorney-client relationship. The answering attorney is licensed in Pennsylvania and all answers are given pursuant to Pennsylvania law, unless otherwise indicated.
Your absences might have triggered rights under the FMLA if you were an eligible employee. I suggest you consult with a plaintiff's employment lawyer before you send in your appeal. There are very strict time limits to appeal the determination so make sure you do not miss deadlines.