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Hello, this is Dr. Jess. I am sorry to hear about your trouble with Happy. Based on your description I do not think there is any at home treatment that is going to solve Happy's problems, and any time a dog is having an episode of severe weakness or collapse, it is considered a medical emergency and they should be seen by a veterinarian immediately for exam and treatment. Without being able to examine Happy it is impossible for me to give you a diagnosis/reason for her episodes, but whenever I see a younger dog have periodic episodes of lethargy and sometimes combined with vomiting or anorexia, I worry about a disease called Addison's disease, or hypoadrenocorticism, where the body isn't producing enough steroids on its own. Here is an article about this disease: http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=608
As I said, I cannot tell you if this is what she has without examining her and performing testing, but it is something I worry about in these cases and she should be seen immediately, because it can become life threatening. The vet will need to examine her thoroughly, listen to her heart and lungs to ensure there isn't an underlying heart condition that could be causing her weakness and collapse, and likely do bloodwork to check for an underlying disease like Addison's.
Until you are able to get your dog into the vet (as I said, she needs to be seen ASAP, as in if an emergency clinic is available to you, bring her in tonight), keep her wrapped in a warm blanket or towel in case she is having trouble regulating her body temperature. If she hasn't been eating today, you can also rub some karo syrup or honey on her gums in case she may have low blood sugar. And then get her in to be seen ASAP. Best of luck to you!