You MUST at least "appear" to avoid them obtaining a default judgment against you. If you cannot afford a lawyer, at least send a letter to the lawyer representing Valley Medical and say that your representing yourself. Send that certified mail, return receipt requested. And also send a copy to the court clerk and ask that it be filed in the court record. Be sure to indicate the case name and case number.
You should also call the lawyer for Valley and see if there is any chance of working something out. And, look further into the Charity Care program that you referred to.