You can add the following trigger using cmsh on your active head node:
# cmsh
% monitoring trigger
% add node_down
% expression
% set measurables devicestatus
% set value down
% set operator ==
% ..
% ..
% set enteractions send\ e-mail\ to\ administrators
% commit
Now all contacts listed in the Administrator E-mail property in Bright will receive an email whenever a node enters the DOWN status.
Conversely, to have those same people receive an email whenever a node goes back UP:
# cmsh
% monitoring trigger
% add node_up
% expression
% set measurables devicestatus
% set value up
% set operator ==
% ..
% ..
% set enteractions send\ e-mail\ to\ administrators
% set markentityasfailed no
% commit