13 week old suddenly startling/waking repeatedly during daytime naps

[HJBeans]

For the last several days my 13 week old DS, who is a great sleeper at night and had napped well during the day when he could be encouraged to start sleeping, has been startling awake every 5-10 minutes or so. He'll startle, begin to cry / wail, and will eventually wake up unless I comfort him with some shushing and a hand on his belly or holding his hands. If I'm here to comfort, and sometimes even if not, he'll go down for another 5-10 minutes.

Has anyone experienced the same at this age?

I really feel for him as he's not getting good quality sleep and is suffering by the afternoon from overtiredness. But as it's completely new behaviour I don't know how to help him.

My ds did this for a couple of weeks at his last nap of the day. I think when he was about 16 weeks. From watching him closely I now think he may have been having bad dreams. He got so so upset. I figured that his little brain must just have been trying so hard to process everything that he was learning/experiencing it manifested during his sleep. Not sure how much help that is but I've very much realized that the phrase 'this too shall pass' really helped. They go through so many funny little phases and changes when they are little but they are just that and more often than not it passes within a couple of weeks and they are back to normal.