Where you holding the tool low with your right hand? Could be just blood collecting in the low hand, though the short period is strange.
While backpacking many, myself included, will have the hands swell due to the hands staying low most the time and being fairly inert. Doesn't happen while running as you pump your arms or when I work all day on the jobsite swinging/lifting.
Possible the vibration could have sped up the process.
The itching also matches... probably not it but if it goes away fairly quick, maybe.
Kent
