Wrong dose taken. 2 days. please advise.

Hello Doctor, my  80 years old mother was having itching in both his hands and gradually it was covering her whole body. I took him to  most rated Neurologist on Practo and he prescribed Mygaba NT(100). Doctor was also keeping medicines at his clinic so I bought it from there only. However, my mother was feeling too much sleepy and dizziness and constipated for 2 days since I gave her medicine. However, i found that I have been given medicine of 400 mg dose. I asked same from the Doctor whether I should purchase medicine in 100 mg dose as prescribed by him. But he didn't reply. I am going to give him same medicine in 100g dose. Hope there will be no measure adverse reactions of this high dose taken for 2 days. Please advise.