You don't need borrow one, you can buy one for less than £6 (free p&p).
http://www.ebay.co.uk/itm/Digital-Tens-Machine-Therapy-Full-Body-Massage-8-Modes-Pain-Relief-Acupuncture-/252620106976?epid=2057268915&hash=item3ad154ece0:g:g8kAAOSwXeJYHEkQ
I have one of these; what is good about it is that it has 8 different programs (giving differing sensations) with random/repetitive pulsing, each having 15 levels of intensity – whereas many more expensive machines are far more limited in providing a variation in their output.
Based on my own experience of using tens machines, they work by inducing a pain/sensation at another location, masking the original pain.
So if you have a pain in your ankle and cut off your right arm – your ankle pain will appear to have gone away (or at least be of no concern to you).