Behavior Regression, due to the stress of a family members illness?

Today I tried alone (very stupidly) to bring my little boy to a pumpkin patch.  DS is attracted (I'm not even stretching this truth) to water like a magnet.  If there is a fountain, a bird bath, etc.  he seems to find it and run to it.

I couldn't get him to focus on  searching for a pumpkin patch, nor to even follow me to eat lunch...where ever I went, he went the opposite direction.  When I tried to gently persuade him to come with me...he would fall to the ground as though I'm making him walk on hot coals or something...I left the patch without a pumpkin and frazzled.   

Jump to...LUNCH.  I went to lunch with my mother, and it was meltdown central.  He refused to eat (hasn't eating anything more than a snack before lunch and a juice)...he was screaming in the family friendly restaurant.  Nothing would make him happy...I apologized at the end (we took out takeout.) to the owner as well as the waitress who I snapped at because she wouldn't get a high chair after it was requested. 

I'm expected to be at a huge 300 person BBQ with DS, but in all honesty I'm ready to throw in the towel...if I don't go with DH then I won't go.  DH won't be there though, due to work...so its simply to hard lately to take DS anywhere alone - for the past three days.

The week prior, there wasn't one issue.  I took him alone to places, without a fight, he would follow me every where...and was very polite.  Now?  Its close to 3-4 time outs a day - he is defiant and strong willed.  He's always been so...but I thought his behavior was very much improved until 3 days ago.

Can behavior regression occur due to family illness?  My grandmother's illness (end stage Alzehimers) is taking a toll on me mentally - and I am beyond what is a normal amount of stress.  I'm finding myself crying/yelling at something that in the past wouldn't bother me.