Soft spot

After my sons bath last night I was brushing his hair and I rubbed my hand across his head and I felt a pulse in his soft spot, it freaked me out but everything I have read says it's normal but I haven't felt it before. It's not sunken in or swollen and I was told to only worry if it gets swollen and it's not. Has anyone else felt this? Is it normal or should I call the pediatrician? He's acting normal and doesn't act uncomfortable at all. I'm just a worry wart sometimes.