My 7 month old suffers with a high case of separation anxiety so obviously, we were very scared of leaving him at a boarding for 4 whole days but there was no other option. He has been back since last evening (been almost 24 hours now). He's lost weight, the part above his eyes was swollen due to a tick bite (thankfully no fever as per the vet), and he's not eating his kibble. He ignored us completely yesterday but seemed very upbeat today, in the morning. No incidents on the morning walk, though he didn't run like he usually does.

But since the last few hours, it's been a completely different story. Seemed like he didn't want to go out, he's hardly had any water all day, he snapped at me when I tried to give him a boiled egg. He came up with me to his playing spot (the balcony on my building) but didn't play at all. Later he snapped at the trainer/behaviourist who has been coming to our place since the last 2 months and is currently working on his separation anxiety. He bit him and was constantly showing him his teeth. He is sleeping now and seems extremely lethargic and unenergetic (usually is full flow and crazy energy at this time of the day).

Has anyone had similar experiences with boarding? Should I be concerned about his health? Should I take him to a vet again if he is still the same way tomorrow or should I wait a while longer? He's a very timid puppy and has a tendency to snap without giving signs because he is very defensive, so it becomes very tough to manage him when he's scared. Will this behaviour go away in a few days and when should I start considering this as a health issue?