Reverse example. Doing a night shore dive with a private guide in Greece. Part way through the dive as we started to head back she was right next to me so I moved over thinking I was crowding her. After about three times she finally got my attention. Wanted to air share. She took my alternate and we swam like that for awhile. Then she went back on her own tank. Talking afterwards I found out that she has accidentally grabbed the wrong tank which was only partly full. Figured as a typical tourist air hog it would be enough. When she realized the dive would be longer she was finally able to get my attention. Was a nice dive.