Welcome to Just answer !
Well you see ataxia / imbalance / incoordination of movements are among the early signs of lithium toxicity along with nausea, vomiting , stomach pain , diarrhea, etc , so in your case the dosage of lithium was increased rather rapidly within a short duration , so this may have lead to it's serum levels going beyond the safe therapeutic upper limit of 1.2 meq/l and hence these symptoms have developed which actually are signs worth noticing and reporting immediately to your treating doctor as these symptoms have the potential to become life threatening if ignored.
So I reckon that you immediately consult your doctor and report the onset of ataxia so that immediate intervention can be employed by your doctor at this time when there is a good chance of recovery by either reducing the dose or stopping the drug altogether.
I hope this helps.
Wish you all the best.
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