Can I drop a hint of advice. Beware recommendations from the old hands talking about having had "a ball" or "just about to retire, no regrets, yes it was tiring but good money, go for it". That advice is now defunct. They joined in the era of different times and found themselves on the gravy train and high up the seniority/pay scales/ rostering agreements and have been shielded from the reality of finding themselves out on the street post redundancy seeing what it's like to start from scratch under today's terms, Those terms they enjoyed are just about to be overturned as they retire.
Everyone can tell you about what it was like in the past or how it is now but no one (we'd all like to know) can tell you what it will be like during your career time. A clue is its heading one way rather quickly. We're now at levels where trains drivers pull in more than a lot of pilots and have better hours and pensions, or contracts. Monarch, BA. They've all had changes the last year. Don't fool yourself thinking it will stop there. Fine, if the Job costs you nowt to get in but it doesn't.
And yes it's very fatiguing. I've done seriously long hours of manual labor in a past life and although felt tired, never knew what true fatigue was. I thought I did in an arrogant way as I had experienced hard graft but little did I know how
by a train you could feel after years of airline flying, I've done short, medium and long haul and it all takes it out of you. Maybe not in the old days when you had decent rest but with min rest and shifts/ night turns/stress/family pressures it all takes its toll.