Thanks everyone.
It started on the night between Friday and Saturday, when he started to vomit and all of a sudden had diarreha. He didn't eat much in the morning on Saturday or throughout the day, just layed down sleeping. Then around 6 pm on Saturday evening he got up and went out to the food in the kitchen but acted really weird not eating. Then he started to stagger around all over the apartment in the most strange way all out of contact. At first I thought he had a hypo, so I poured dextrose into him, and then tested his bg, and my meter read 6.6 mmol, 119, which isn't alarming but lead me to think that he was lower before I gave him all the dextrose. He was really out of it, and I also took his temperature which on my temp showed high temperature. Because he had vomitted and had diarreha in the night, I also thought he might have an infection, and I had some antibiotics at home and gave him a half as it said on it. But he kept staggering around all over the apartment, not making contact with me, and then he started to breath with his mouth open, which isn't a good sign in cats. It was if he really was fighting for his life. So I went straight into ER with him at the animal hospital. When they came at 8pm to take the emergency blood test, he hadn't changed, and was so out of it he didn't even react to the needle pain as he normally do. And on that blood test it showed he now had 3.3 mmol, 59, and that is very low for him. And in spite all the dextrose I had poured into him. When the vet came she also checked his eyes, and the pupils didn't contract, so she suspected high blood pressure. He was admitted and put in an oxygene cage at Intensive Care, with iv fluids with glucose, and I left. They also measured his blood pressure but it was 138, which is normal, so that wasn't the cause then.
They've done xray of his lungs which showed normal, ultrasound of his abdomen which showed nothing, they took sterile bladder urine test to see if there was an urine infection but that test was normal, but on the large blood test it showed infection. But they really don't know what is wrong with him.
He was supposed to come home today Tuesday, but they called this morning and said he had vomitted and had diarreha again and also been low in the blood sugar, so they are keeping him and will call again tomorrow. They will also call if any changes so I can come in.