A diagnosis and prescription is necessary for a CPAP or BiPAP machine. It is NOT recommended to loan or purchase a machine without a diagnosis as there can be contraindications which is why these are prescription items! Also bear in mind, machines on loan elsewhere will have been previously used by other people and are unlikely to have been adequately sanitised.
There are also different types of machines such as CPAP, BiPAP and Non-Invasive Ventilation and it is important that people are issued with the correct machine, dependent on their medical history and specific diagnosis.