Dogs never starve themselves to death. A dog that is sick, injured or in pain loses appetite. Achange in the environment is another factor. You have tried to bring him together with hissister and that did not help so that cannot be a factor.A dog may not be able to keep down food because it may have eaten somethingdisagreeable or eaten too much too fast. It can also indicate something as serious asswallowing a toxic substance, or a condition that requires immediate medical attention.In a situation like this, the first thing you should do is take him to a vet. The vet will check forparasites and his general health and want to get blood work done. When you visit your vetbe prepared to answer questions related to the length of time that your dog has beenrefusing food and stool frequency and appearance.Very often we cause the problem by getting anxious about the food we provide. Pets thenbecome picky.A healthy Gerbarian Shepsky will always eat when it is hungry. Why don’t you try feeding itat select times? You could remove the food until the next feeding time. This may encouragehim to feed better.You seem to have recently acquired the pet. In this case, you must have checked on thehealth of the dog’s parents. Congenital diseases from either parent, though uncommon isstill possible. A dog can develop a sensitive tummy due to sudden relocation which makes itnervous. Bringing your pet together with its sister may not have calmed its nerves.You own a breed that is a crossbreed of the German shepherd and the Siberian husky. Boththese breeds are very popular as pets. There are certain diseases that they may haveacquired from the parents. These diseases may cause loss of appetite and lethargy.Two reasons to feel lethargic are Hypothyroidism and Cushing’s disease. A GerbarianShepsky can suffer from these disorders which cause glands to underproduce necessaryhormones. This can cause lethargy and a dull coat. Your doctor will ask you to do a full bloodpanel to detect a thyroid disorder. You must remember that hypothyroidism is incurable butcan be controlled with medicine.Another test that you could do in case of loss of appetite is the Exocrine PancreaticInsufficiency. Exocrine pancreatic insufficiency is a condition in which enough pancreaticjuices are not produced. This causes the inability to digest fats, carbohydrates and proteins.A dog loses weight due to poor digestion and malabsorption of nutrients. A GerbarianShepsky is often a victim of this disease so it is best to get the test done.The best suggestion is that take your pet to a vet to rule out any serious issue. Even if thereis an issue your vet can deal with it if you go immediately. You have said you are scared. Thiscould be another reason why your pet is reacting in this way. Your pet feels yournervousness and this is causing it to get nervous. This may prevent the intake of food andnaturally, it has no energy.