If the person was clearly having trouble, I would probably lend a hand unless he or she strictly told me not to.
If the person was near Dazedness, I would wait until he or she fainted and fend off the monsters so said person could recover (and so I could get some serious EXP). I probably wouldn't heal them unless they asked me to; some people have "pride" issues in that regard, and I don't want to make a reputation as the Dignity Slayer.
Or maybe I do. twisted
(On the other hand, I could heal them and then explain that I'm just using them as target practice to build EXP. That could work.)
If, however, they were not near Dazedness, but clearly needed (or asked for) help, I would assist them in any way that I was able, including, but not limited to: fighting the monsters, healing them, healing me, and hauling both our butts back to the nearest Moonfield, if possible.
(Fun fact: "Moonfield" is the translated surname of popular anime character Tsukino Usagi. While the name was meant to imply "rabbit of the moon", the kanji for "field" was used instead of the kana "no", the possessive suffix.
Another fun fact: Japanese are very fond of name puns in their cartoons.)