Is your plant indoors? In general, they do well with basic indoor plant care, i.e. bright, indirect light, with an hour or two of early morning or late evening sun. They like typical indoor temperatures, which means not below 60Ã‚Âº F. They like evenly moist soil. For me, that means that if the surface of the soil feels cool to the touch, I don't water it.
They don't live very long indoors, as a rule, a couple of years on average, I think. They don't get very large when grown indoors in containers, either.
If yours is losing leaves, I would first check for red spider mites. Mimosa pudica
tends to be prone to infestations of them. Small strands of webbing are the giveaway for spider mites. They can be killed by spraying with a soap solution. Spray the plant until it is dripping, being sure to get all surfaces. Wait 5 to 7 days, then repeat the treatment. Do this 4 to 5 times, and it should clear the infestation.
The second thing I would check for would be root rot. You can gently slide the plant out of its pot and look at the roots. If they look brown and mushy, then root rot has set in. Since these plants sprout easily from seed, I would just replace the plant. I don't know of a dependable way to cure root rot, especially if it's so long standing that the plant has lost its leaves.
If the roots look healthy, but wrap around and around inside the walls of the pot, it would be time to move it to a larger container. Select a container no more than 1 size larger than the old one.
Does that help?
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams