When is it ok to have an adult meltdown/breakdown?

Heidi
Please bear with my rant of questions...
Is it ever ok to ask for help when you are just trying to be strong?  How do you not seem weak or striving for attention?
Is it ok to demand a break when you're a mother, a wife?
--When is it ok to slow down when all the world wants is for you to speed up?
Is it ok after your child (infant in age) has a brain tumor that requires hospitalization and multiple surgeries?
How about after your husband is diagnosed with leukemia?
What about when your other child is found to be on the autism spectrum?
When dealing with secondary infertility?--
The saying is "God only gives you what you can handle in life."
At what point are you able to say...fuck this!  I cannot handle anything else!  I am done being a warrior!  I am over being the strong one!  I did not ask for this!  I have focused on the positives for this long now, I've been optimistic!  Just let me crawl in a hole and hide!
Is it ok at a certain point to throw your hands in the air and not have everyone around you expect you to be ok for a while?  
Is it ok if I just check out of life for a period of time and let someone else take on my adult responsibilities??