Since we do attachment parenting, I had no trouble with my dd needing a lot of support going to sleep (nursing to sleep, sharing our bed, having someone lie down with her, etc.). Unlike my other kids, she prefers absolute darkness, no distractions, quiet, and closed doors. (I think it's really important to figure out what works for each of them.) But later on, long after she was happy sleeping in her own bed, she said it was hard to get to sleep. She definitely has anxiety issues and her teacher described it as "looping": turning things over and over in her mind. She explained it to me in some detail. Her psychologist suggested melatonin, but I also felt we needed to change her bedtime routine after a relaxed summer. She still goes to bed late, because she really can't relax until she's finished all her work, but she has made good progress in managing her stress and being able to sleep.
J.