Thanks everyone for your responses!
Yes, I think it is a guilt thing, coupled with a lack of understanding of what constitutes "activity" for a bub. For us grown ups, activity really does need to be an all-singing, all-dancing affair to keep us amused, but I can see that for my lo, the simple goings-on of life are plenty amusement/education enough!
I have been trying to get outside every day or two to lie with Tyson on the grass on a rug, to enjoy the lovely summer weather, and to interact with our 4 dogs, who think he is the best thing ever. That seems to be a favourite with both Tyson AND the dogs, so that is a hit, but we need to take care as some of the days are very hot this time of year.
Once again, thanks for your comments!