help my oscar lulu has a large protruding eye,ita happend overnight,there are no other fish in the tank

Could you please post a photograph? Next you need to test your water for ammonia, nitrite, nitrates and pH. This could possibly be due to trauma, maybe the Oscar asked itself during the night. However, the symptoms you describe do rather sound like Popeye disease. This is often caused by a bacterial infection of the eye. It is treatable if caught early. Keep us posted

Im with OFL, we need a pic but it sounds like pop eye. The treamtent is any anti bacterial (it will usually say on the container that it treats pop eye). Follow the instructions carefully and remove any carbon from filter. If the eye isnt back to normal after once treatment then retreat. But we do need that pic and test results ASAP