PLease help

I am 41 years old. This is my story. I graduated 1995 with a BS in Exercise Science- I worked in the field for a few years- and LOVED it (retreat for obese women, personal trainer, fitness club director). I got married and had three wonderful children. SO, I have been a stay at home mom for ten years. My youngest will start Kindergarten this Fall. I want desperately to go back to work, but realize after being away for so long, I need to go back to school if I want any sort of job satisfaction/money. Fitness/Health jobs are scarce and do not pay well- I found this out only after starting a Masters program in Exercise Physiology. The job prospects made me leave the program. So...I tried to figure out what I could do...I ended up at a local community college for Echocardiography- after speaking with the department head, realized the program was not accredited and didnt even know if it would continue. So, again I was left confused about which direction to go in...I thought about Physical Therapist Assistant, because of my EP background, but the market here is a bit saturated and I still keep coming back to my love of cardiac physiology. I had originally wanted to work as an EP in a cardiac rehab facility. SO after researching a bit, I came across cardiac rehab nursing. It looked as though I could specialize , still work in my area of interest, (or even go hardcore cardiac nursing, cath lab, etc.- all interest me). SO I got excited at the idea of it all. This is my problem...I am so scared about returning to school for this profession. I have taken recent masters level and undergrad. courses in Med. Physiology, re-took A&P because mine was "too old to be accepted", Medical Terminology, Exercise for SPecial POopulations, EKG interpretation... I got A's in every class. My problem is that taking these courses- one or two at a time resulted in extreme stress for me( had to get an A type person) and it was very difficult to tend to my kids and study, be a wife, etc...I was able to spit out the info in order to get a good grade, but I feel as though I didnt retain a thing!! This makes me nervous when it comes to nursing, as I know RETAINING the info is a must. What is wrong with me? Do you retain more as you work on the job? How do you remember EVERYTHING?! My next concern is that I have a family and I am not sure if as a new grad I will be forced to to 2nd or 3rd shift- this wont work for me- my kids are still young. (11,9, and 5) My husband owns a restaurant and it is a mom/pop operation. We do everything for very little money. He is gone alot in the evening as he cooks and runs the place, so I need a daytime job- one that pays well. I am also worried that since I want to specialize I will be stuck working every floor for ten years before I can work where I want. I love helping others, I have a strong interest in cardiac physiology and cardiac rehab. Is this the career for me? Can I do this and still be here for my family? After spending money and switching majors, I need to be sure this is it. My worst fear is to spend the money and get half way through and change my mind or see it isnt for me. Any advice/help/info is greatly appreciated!!