Found something here under the header 'Sync Terminal'. Looks like possible shock is normal when connecting a camera hot shoe to a flash unit (even it's a battery operated flash).
http://www.mir.com.my/rb/photography/hardwares/classics/nikkormat/elseries/el2/flash.htm
http://www.mir.com.my/rb/photography/hardwares/classics/nikkormat/elseries/el2/flash.htm