I had depression and anxiety when DS was a baby.
At one point It was hard to get my DH to understand that I was in a crisis, as he had got used to me being unwell and I just couldn't share with him how very dark my thoughts had become.
I phoned my GP surgery one morning, receptionist wanted to know whether I needed an urgent appointment. All I said was that I was feeling very desperate and frightened and needed help. This woman (who to be honest is renowned for being a bit of a dragon) was so kind and helpful and the Dr phoned me back within 30 mins and was at the house within an hour, and phoned DH at work to get him home until the MH crisis team arrived.
I'm only telling you this because for me it was a turning point, and although it took some time to get totally better, if I hadn't made that call I'm sure the outcome for me might have been very different.
It is very hard to take that first step, and there are many different ways that first step can be taken. Whether it is going to see your GP, phoning Pandas, phoning OOH health care service or any of the other useful suggestions on this thread.
Taking that step to tell someone, who is professionally trained to help, how very desperate you feel is what you need to do today or tomorrow.