Jampanda
Thanks for all your comments, as I said previously we have backed off and have had no contact in the last six weeks. We actually came back from the cruise over 11 weeks ago. It was a long cruise 5 weeks, Hubby and I had booked first when our friends decided to come with us. We definitely didn't spend much time together onboard as we all like to do different things, we mainly met up for meals and days ashore as they weren't confident to go ashore on their own. As I mentioned that we were all ill at the end of the trip, no idea what it was- some awful virus. I was actually the worst and ended up with pneumonia. Our friends helped us get home and we haven't seen anything of them since, and only had very basic contact for the first few weeks. We can't pinpoint anything that actually happened on the cruise that could have caused a problem, only that they seemed to become disappointed and grumpy but we put that down to being poorly.
Obviously there's a reason why this couple now feel 'claustrophobic' about daily chats which presumably they once were happy to engage with.
I think you have to accept that you might never know the reason though.
It could be something said or done during the cruise, or it could be that the daily chats have now become onerous - or both.
Whatever the reason, the ball is in their court.
It may be that the cruise didn't turn out the way they'd hoped - and the nasty germ or virus you all caught obviously didn't help matters. Whatever the reason for the cooling off I don't think it's worthwhile going over the details in your head, sometimes these things are too nuanced to decipher. It could, for example, be that some remark made by you or your DH upset them (or one of them) - something you won't even remember; on the other hand, it might just as easily be a general feeling of disappointment with the holiday. And nothing really to do with you.
Being told that your regular chats make them feel claustrophobic is something of a mild shock. I've never experienced similar, but, I have felt the pressure from a friend who became too 'full-on' and told her so. The real reason I couldn't cope with it though was nothing to do with her - it was just that there was too much going on in my own life at the time, and any outside pressure made me feel 'claustrophobic'.
... so it might even not be a reflection on you, is what I'm suggesting!
A couple of posters have suggested that you 'phone them, to make sure they are OK. Unless they are a couple without family or other friends, I'd not recommend it - if the chats are making them feel claustrophobic, then a 'phone call will just add to the feeling of being pressurised.
In your position, I'd send a really brief message telling that you quite understand, and wish them well. One sentence, nothing more.
Then it's up to them to respond - or not.