Hello,
Handshaking or tremors YouTube various reasons. Some of the common reasons are anxiety, medications, old age etc.
In your case, since you are using Lithium, and lithium is known to cause Tremors.
Next Steps
1. Get your Serum Lithium levela checked
2. consultant your psychiatrist
3. take a opinion from neurologist, specialised in movement disorder.
Health Tips
rule out lithuim related tremors, ASAP
if any, rule out other causes