Jamie Hanrahan gave an excellent answer but I think there is another possibility apart from what he described. It seems that many people have zapping issues with their laptops and the zaps seem to be more than just static. See this page for a lot of examples
From that same page, a user responded with the following (and I quote):
"If you have the laptop in your lap, and if you are wearing shorts,
the areas of your legs that are in contact with the screws will feel
uncomfortably tingly - like there are pins being poked into the
surface of your skin, but not deeply. The sweatier you are, the more
galvanic reaction (the more it hurts). This is NOT a power supply
problem, so getting another DC power supply is not going to cure the
What this is, is the AC voltage that is sinked to ground through a
number of circuits that rely on higher voltages stepped up through DC
to DC converters (see:
http://en.wikipedia.org/wiki/DC-to-DC_converter). Displays take higher
voltages to operate. An oscillator converts the laptop's DC voltage to
AC, steps up the voltage, rectifies it, then filters it. This is the
residual AC voltage from that process. It is a byproduct of
miniaturization and not having enough space for adequate shielding or
having an adequate groundplane. You become part of the ground and
might be a better ground than the rest of the device.
As the OP stated, 48 mA is usually not enough to disrupt your heart's
electrical activity, but it is a big discomfort. At first, I used a
book under the laptop. Then I took some black electrical tape and put
it over each of the screws on the bottom of my Dell. It works, but
then, the laptop also gets hot. That's another issue."
Connecting a crocodile clip between my network cable and a ground did fix the problem...HOWEVER AS MENTIONED BY OTHERS, YOU SHOULD NEVER MESS WITH ELECTRICITY WITHOUT PROFESSIONAL HELP. For example, if the AC adapter is leaking AC (as suggested by Jamie) and you touch the crocodile clip, YOU COULD BE ELECTROCUTED.
Here is a page describing similar ways to ground your laptop. AGAIN, ALTHOUGH IT MAY APPEAR SAFE, IT CAN BE VERY DANGEROUS TO EXPERIMENT WITH THESE DESCRIBED METHODS WITHOUT PROFESSIONAL HELP.