Is this anxiety of a digestive issue

My 4yo JRT and Pomeranian mix started having these evening episodes where he wants to be held all of a sudden and when you hold him he either tenses up or becomes a sack of potatoes. If you leave him to lie down next to you he would not fall asleep and just stare, unless you give him a spasmolytic or probiotic and wait an hour or two for the drug to take effect so he would fall asleep. In the morning he would behave like nothing happened. When we go for a check up at the vet everything would seems fine – no painful stomach and no gas.

I've been giving him probiotics and special gastro kibble divided into four small meals so it would be easier for his stomach. With the new probiotics and kibble the episodes have become more far inbetween. When he experienced one a couple of weeks ago it was after he let out a loud fart and visibly got scared, the weird behavior kicked in and he wanted to be held. So, I was like: does he just get super anxious because he has gas? Well, what can I even do about that? My other theory is that it happens when he hasn't had enough exercise because of either the weather outside or because he has grown bored of our games, so he reaches a point in the evening where he doesn't know how to calm down and the anxiety kicks in.

It only happens in the evening. During the day the behaves normal, as well as during our walk after a get off work. As a JRT mix he needs a lot of play (normally till at least 10 pm), so even in days when he experiences an episode he would play and run a lot in the early hours of the evening. But when he needs to stop playing for a bit because we have to sit down and eat dinner or I have to go to the bathroom he would all of a sudden start looking for comfort, trying to force his way into your lap or scratching at you to pick him up with ears back and tail between his legs.

I'm at my wits ends and I don't know how to approach this anymore. Has anyone else experienced something similar with their pooch?

Edit: The title was supposed to be "Is this anxiety OR a digestive issue".