I have given birth twice, most recently 8 weeks ago, at home.
My first was at a Midwife Led Unit, but both in water, and I have positive memories of each one.
For me I knew I was in labour because of having very strong contractions. I would describe them as very strong cramps that increase in intensity and then fade.
The sensation seems to come from around your back and pelvis area and they are different to period cramps because they have a pulsing sort of pattern to them rather than the dull ache you have during a period. But there is similarity to the sensation. The pain is uncomfortable and can be all encompassing, particularly when they're closer together and towards the beginning of the second stage.
My first baby I woke up at 2am with these sensations and that was my first sign of labour proper. The second baby my waters broke 7 hours prior to having any contractions but I would still say the contractions were when labour started.
The old cliche that giving birth is like feeling that you need to do a really big poo is very true and for the second stage that is exactly what it feels like with a bit of stinging going on if you have any tears