callmewhatyoulike - I've so been there.
PND after ds (nearly 6) was born. Wasn't an overdose, I used to quite methodically plan when I'd walk out the house in onto the really busy main road near our house. Would have the timing all worked out so that H was due home from work and ds would only b alone in the house for a few minutes.
Terrified myself and would phone H hysterical telling him to get home now.
Sweetie its awful... I know how you feel and there are loads of MNers that do too....