Brief Answer:
Probable stroke, should seek medical help.

Detailed Answer:
I read your query and I understand your concern.

Since you state that the weakness you are feeling did not improve overnight I assume that it was installed in an abrupt manner.

In that case the most probable diagnosis is a stroke. A stroke is related to brain damage due to either ischemia (a blockage of a blood vessel causing lack of blood supply to the area it supplies) or a hemorrhage (rupture of a blood vessel and bleeding). The damage to that area manifests itself commonly of the limbs on the other side, so in your case the right side of the brain.

The most usual lesion is an ischemic stroke, but symptoms can be similar, only brain imaging can put a definite diagnosis. So you must seek urgent medical attention to be evaluated and undergo necessary tests like brain CT and MRI. Those tests would confirm the diagnosis (excluding other possible causes like tumor, infection etc) and indicate the scale of the damage.

Afterwards other tests should be required to determine the origin like heart rhythm studies, heart ultrasound, ultrasound of the neck vessels, complete blood count and biochemical lab tests to look especially for diabetes and lipid panel. Other tests might be required, depends on the findings.

Most often at your age, stroke is related to heart conditions, atherosclerotic impairment of blood vessels due to factors like diabetes, high blood pressure, smoking, obesity, high cholesterol etc. There are other rarer causes to investigate if in doubt. At times cause isn't that easy to find.

Treatment, depending on the results of the tests, will consist in taking measures to address the cause and the risk factors as well as in blood thinners if it's ischemia in order to reduce the risk of other strokes in the future. If there are other complications like say infections, heart or respiratory difficulty those will be addressed as well.

So I repeat that you should seek urgent medical attention, not only for the current weakness but also to prevent more serious recurrences and complications.

For your current weakness physical therapy must be started, it is a gradual process but over weeks and months there will be improvement.

I remain at your disposal for further questions.

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