Go ahead and try volunteering. It will help you better define what you can and cannot do, and about your stamina too. On the sadder side, you might not be able to do the first volunteering job you try. I've been fired from just such tries.
I've heard what the others are saying, ssi doesn't care as long as you aren't making money... but I think if you end up with skills that could transfer into a real job, with hours of 30 or more a week.. consistently, well then you might need to reevaulate at that time if you might be able to find work that pays.
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meditation is a true way to connect to the Source </font color=blue>