It may be due to degenerative changes progressing in your spine. Numbness can be due to pinched nerve. You can consult a physiotherapist and can learn nerve mobilization exercises which will be helpful in reducing numbness.
Next Steps
Consult a good physiotherapist for early recovery and overall assessment. You can get a Nerve Conduction Velocity test for a better picture.
Health Tips
Avoid bad postural habits. Keep your limb supported while sleeping.