I've seen a couple of little quirks at the beginning of tachanun and I'm looking for sources... They may or may not be related.
- Just before putting their head down, I've seen some people who give their chest a single hit. Is there any source for this?
- Also, it seems that most people put their head down before saying ויאמר דויד אל גד. This is what a sample of artscroll siddurim seem to say. However, I have seen other siddurim that have that passuk before the instruction to put your head down. This alternative minhag seems to somewhat correspond with us saying "נפלה נא ביד השם" and then subsequently falling on our heads. Are there sources for these different minhagim?