BME & medicine are wildly different, whilst both operate within the healthcare sphere the natures of the roles and projects are fundamentally different.
As an industry biomedical engineering is going to more closely resemble mechanical, manufacturing & materials engineering & whilst consumer related factors will be fundamental to projects ultimately the engagement will be fundamentally different.
As an engineer how much desk time you spend will depend on your exact position but in a professional role you will primarily be office based, particularly as you get more senior positions.