Recently Seperated Sad Hamster

[HamsterBubu]

Hi guys
We recently separated our two male dwarf hamsters Cookie & Oreo. They'd been living together since we got them (they were from the same litter) but we had to separate them around 3 days ago after it became clear that they could no longer tolerate each other as Cookie was bullying Oreo and it escalated quite quickly. Cookie remained in the original Bin Cage and he has been absolutely fine and already appears to be miles happier than he was while living with his brother. Oreo was moved to a new bin cage, but ever since we moved him he appears to be really down. He is constantly in his hideout and will pop his head out to take a treat but apart from that we wont see him. It does appear that he is a little bit more active while we are sleeping, as we can see that there was been some activity around his wheel or where we have scattered his food. We are worried about him, as usually he is a very cheeky and energetic hamster and its not usual for him to be acting this way. Does anyone have any suggestions or advice on if this is normal or how we can help him adjust any better?