I've looked at definitions of both "passionate" and "passional", and they are pretty much the same, but I can't help but feel being passionate is different from being passional
I had to look up "passional," as I've never heard it used this way. "Passionate" is the normal way of describing something having a lot of passion: passionate lovers, a passionate interest in astronomy.
"Passional" means "of or relating to passion" rather than "filled with passion," and might be used if you were academically describing the effects of passion as opposed to some other factor. Passional is also a noun referring to certain Christian texts, which may well be its most common use.
99% of the time, "passionate" is the right word and "passional" will get you funny looks.