a. Help yourself when you are feeling suicidal Read the one above first. This has some practical ways to help, in addition to contacting an expert. http://www.psycom.net/depression.central.helpself.html
b The Samaritans Charity offering expert support in the UK from volunteers to anyone in crisis (not only suicidal). Phone, email (can be anonymous), letter, face-to-face. http://www.samaritans.org.uk/
c. Suicide Crisis Centre Also includes some good links near the end eg distraction, why live, what its like calling a helpline/hotlines (not a clinic- webpages only) http://suicide.com/suicidecrisiscenter/
d. Panic disorder An expert source. The fear you feel doesn't mean you are in real danger. http://www.nimh.nih.gov/health/topics/panic-disorder/index.shtml
f. What to do if someone you know is suicidal A practical, clear guide. Focuses more on how to pick up the risk than what to do (apart from getting help). http://www.mayoclinic.com/health/suicide/MH00058