I got caught in a rainstorm in one once. Definitely did not keep me or my stuff dry, the tarp blocks the rain from the top, but you get wet air blowing in from every other direction, and a little bit of spray comes in both ends.
I've been caught in the rain and I was fine. I read online that you can get a rain fly that folds around the edges and closes up the ends and keeps out spray and such.
I imagine in a rainstorm you'd be pretty miserable in a tent too, depending on where you were in relation to running ground water 🤷♂️
I have felt vulnerable yes, I had one experience where I woke up and thought I heard my buddy walking through the leaves, but then I heard him still snoring. I got a little freaked out, and listened closely, I was just hearing things.
But maybe I would've felt the same in a tent? Maybe it was just because I was out in the middle of nowhere, which was new for me.
Could be, but what if it was a cougar or something? Having my underside exposed like that, and no quick/easy way out, feels more dangerous somehow (I know it probably isn't more dangerous than a tent hypothetically, but it feels that way in my mind).
I often roll over from my back onto my side and it works fairly well! I would recommend a longer, wider hammock. 11 or 12 feet in length and just “wide” labeled hammocks from any cottage vendor. I would recommend a pillow as well. I have used both the thermarest memory foam pillow (bulkier and heavier) and a sea to summit Aeros ultralight with great success.