Ethel and others will respond to your question, telling you that you have sold your soul to your current employer and must do their bidding at all times (even in your free time) � they will even tell you that your current employer can dictate for whom you may work, once you terminate your employment with them.
I look forward to my current employer taking me to court, for having the audacity to work for my next employer (whoever they might be). Similarly, I would very much doubt that my current employer could stop me working, at times I am not employed by them, for someone else (even if they inserted such a clause in my employment contract). Having said that, someone working in the research & development labs for Glaxo, could reasonably be required not to work for Roche in a similar capacity � but I doubt Glaxo could enforce a ban on them working in a local bar (or one that was not local, for that matter).
Given the above, I see no problem with you doing bank work for a hospital, when you normally work as a receptionist � however if Ethel is the HR director or your company, the answer is definitely � No.