Weak legs, muscle twitches, memory loss, vision problems, apathy after the birth of 4th child three years ago. paraneoplastic syndrome?

See your doctor...: Your symptoms (regardless of cause) are of concern and you should be seeking care from a physician to discover the cause. Nobody can diagnose you with paraneoplastic syndrome via computer -nor would you want them to as that is a very rare condition that should be managed by a team of physicians (and is secondary to a cancer - which you have not mentioned). Take care of yourself - see your doctor