@feruze-- I don't think that fatigue and drowsiness are very common side effects of metoclopramide in pets.
Are you giving your dog any other medications?
Metoclopramide can contradict with some medications which can cause sleepiness. Muscle relaxers and pain relievers can cause fatigue and drowsiness and giving metoclopramide along with these can intensify these symptoms.
You might want to ask your vet about this and mention anything else you may be giving your pet.