Is it okay to say and/or? How else might I phrase a sentence like the following 

>  The amount of happiness displayed by
> the bunny increased when either the
> bunny was well fed and/or when the
> bunny was watching a sunset.


I am writing a scientific paper, and it is important that the events have the same effect when they occur separately or together; I have written a trivial example replacing esoteric words with more familiar ones.