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Without further information it is very difficult for me to provide the best advice but I shall certainly try.
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As his signs have persisted more thab 48 hours he is at real risk of dehydration and low blood sugar.
His symptoms aren't specific and could have many causes including a recent toxin ingestion, pancreatitis, hepatitis, gut obstruction etc.
I would advise a vet visit ASAP, even if this means an out of hours clinic. They will examine him and may run some tests such as a blood test and abdominal scan. Treatment will depend on what is going on and may include e.g antibiotics and fluids.
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