When is it too much?

Well done on reaching goal - now it's time to work on body composition to get that six pack. ..try circuit training and strength training, both excellent for tightening everything up.
Forget about trying to lose more weight if it would leave you too thin.
Up your calories by 100 a week til your at recommended maintenence cals.

Wishing you every success on achieving your perfect body ☺

Congratulations! A good healthy wonderful attractive weight won't get you six pack abs. To do that you need an extremely low body fat and work like a dog. I've got two tall skinny muscular kids (young adults) with BMIs of 18. They are as thin as those Abercombie & Fitch models. But only one had obvious abs, and that was when he did situps every day and worked on a farm. When he went into the Peace Corp he came back so thin I could see the bones in his nose but he didn't have obvious abs because he'd given up situps. (Great shoulder muscles though from carrying water.)

Guys who look like that are paid to look like that - it's their full time job. Or they aren't paid and they make it a serious hobby.

You need to make a decision about where to put your time. I think it's really easy when you hit your goal to think you should go further and lose more. But your true goal may be to maintain a healthy weight over a lifetime. Or it may be to lift and look fantastic. But for a while, why don't you try maintaining and learn more about the way you want to move forward with your long term fitness goals?

Just my two cents.

And congratulations!

When I reached my goal weight I was thrilled, then came the massive weight flucations that go with maintaince, it was annoying me, so I decided to slowly a dozen more pounds, so I'm always at least just below my goal instead of at my goal.

I believe being too thin causes miserabley, irriaitibly and depression, if you think you been like that lately more often than normal, then your probably close to it.

I was similiar. I reached my goal weight and like you was so effective at it I thought lets loose another 5 pounds, good lawd, what I saw in the mirror was horrying, I could not believe the difference 5 pounds could make, I looked emaciated and couldn't wait to gain those 5 pounds back. I've been maintaining for 2 years now and alternate my days between cardio and strength. I'm actually 5 pounds heavier than my original goal but my body has never looked better, healthy, strong, defined, toned and only today after my morning run my 9 year old said, '...mom you've got a six pack showing...', I was elated. It's not all in the scales!