When the conditions are right, electric shocks can be fatal even at low voltages.  Since our bodies are approximately 70% water, it is easy for electricity to pass through us in just seconds.  A mild electric shock can cause headache, muscle fatigue or spasms, temporary loss of consciousness and temporary difficulty breathing.  Serious and potentially fatal side effects of electrocution can result in severe burns, vision loss, hearing loss, brain damage, respiratory arrest or failure, cardiac arrest and death. 

Consider the chart below:

Less than 1 MilliampMay not be noticed.
1 MilliampSlight tingle.
5 MilliampsSlight shock; the average person will be able to let to. Strong involuntary actions can result in other injuries (i.e., falling off a ladder).
6 to 25 MilliampsPainful shock; loss of muscle control.
9 to 30 MilliampsPerson may be thrown away from the power source or may not be able to let go.  Again, strong involuntary actions can result in other injuries.
50 to 150 MilliampsExtreme pain, respiratory arrest, severe muscle reactions.  May be fatal.
1.0 to 4.3 AmpsHeart stops.  Muscular contraction and nerve damage may occur.  Likely to be fatal.
10 AmpsCardiac arrest, severe burns and death is expected.
Effects of Electrical Current on the Body