This job is really stressing me out.

I’ve been with the company for 9 years. The last 4 have been in the office dealing with customers in person and on the phone. The last two years have been tough due to management changes and office personnel either quitting or getting fire. They hired two replacements one lasted a week and the other did a no show after 3 months. The office went from 4 people per shift down to 1 and we are still expected to complete all required tasks plus handle extremely busy phone lines. This has taken a tole on me. Three weeks ago, after work, I went to emergency room thinking I was having a heart attack. It turns out it was a panic attack. I did not inform my job that I went. I was embarrassed that I was weak. I know I need to leave this position but I feel terrible about abandoning my coworkers when we are so short staffed. Also my daughter is having a baby and wants me to quit to be with her. In the past, I have tried to quit only for them to talk me into staying. I’m not sure what reason I should give for needing to leave. Tell them the stress is to much or my daughter needs me. And how each would effect any reference or unemployment benefits. Also, how would I explain why I left to possible future employers