I did detox in a local behavioral health (psych) ward of a hospital. It was scary at first but turned out fine. I should say I spent one night in a detox facility prior to that and it was not the best experience. After detox, I went to a rehab for two weeks for alcohol. The program was decent but the population and security were not so good. A lot of fights both verbal and physical. I would recommend not bringing valuables, bringing something to write in (did lots of journalling), and bringing a calling card. Just a few practical suggestions.
I did relapse after rehab but have been sober for 94 days now. Would I have gotten sober without rehab? Don't really know. Kind of think that although I wasn't immediately successful that some of it did stick in the long run. I do agree that it's what I did since then that has made the difference but...it was probably another step towards hitting bottom and then thankfully starting to crawl back up.
I totally understand being nervous. I remember it well. I was both nervous about what was ahead but also anxious about getting started. I really did want to get well. I just didn't know how. I wish you the best; it will be hard but it's so worth it.