End of day sleeps and night waking?

My 2.5yr old is dropping her day sleep, has a day sleep maybe a couple of times a week. She has been a fab sleeper for ages now, and when she has no day sleep she will sleep from 6.15pm till 7am. But the problem I am having is that the days she does not have a sleep she wakes approx 2 - 2.5hours after going to sleep and she is very upset, is consistently at this time and always on days she does not sleep. Sometimes a cuddle is her bedroom will be enough to soothe her, but other times like tonight we had to bring her out to the lounge and distract her to calm her down it was just awful she was so upset. Once calm she is happy enough to go back to bed and sleeps all night. She doesn't want to be awake and is yawning all the time! I don't think it is nightmares or anything as she is happy enough to go to bed and not scared. Any ideas .... just a phase? ....I just hate to see her so upset.

Emma

Yeah I am thinking overtired but unsure what to do about it! I still put her to bed early afternoon so she can go to sleep if she needs to and if not she sits in her beanbag and watches a DVD for an hour so is resting as best as I can get her to rest. Does anybody do a bedtime earlier than 6.15 and still not end up with an early waker?