You took a month off and you have been back one week. What exactly did you expect? Conditioning is a very transitory adaptation. Strength is more persistent. This is another data point to back up that theory.
Work with me here. You want to get better at rowing and right now things don't feel good since you had a month off, so you stopped training. This makes no sense.
I am afraid I don't know. This is above my pay grade. Maybe someone else will chime in.
You put on seven pounds. That is unlikely to kill you on the erg. You didn't row for a month. This is why rowing feels badly right now.
Highly unlikely at this point.
Insomnia is a bitch. Truly. This will fuck your training up badly. However, it seems like you are sleeping more. I recommend getting laid. A lot. Make it your goal to have sex twice a day. Different people, same person, whatever floats your boat. I bet it will help you sleep. Also, get some sun every day. I don't care how cold it is. Since you gave me your weight in stone, I assume you are from England. I realize the sun does not shine there. Ever. But do your best. Let me know if it works.
I don't have insights into why lost your ability to sleep. I do think that there is nothing unusual about your performance drop off, however. You weren't training. Conditioning evaporates quickly. Fortunately, it comes back pretty quickly, too. Also, your training volume, especially on the aerobic side, was pretty damn awful. My close friend, Kelly, would hit me for saying this, but fuck rowing. It's a miserable sport. Also, as a former distance runner myself, fuck running, too. Lay off the cardio for a while. I realize you don't want to hear that. Get your squat up to 330 for 3x5 and your deads to 380 for 1x5. Put on a little more weight. Have as much sex as possible. Become an expert at making women achieve multiple orgasms. Eat lots of meat. Listen to some Bolt Thrower and Paradise Lost while lifting, two fine English bands. Salt liberally with Rammstein and Helmet. Let me know how things are in six months.