Worried about my little bit - falling over

I have a 5 month old "runt" which I've posted about before. She took about 5 weeks to hatch and she appeared to be quite normal, but grew very slowly. She's about a 1/4 of her brother's size now, fully feathered, normal in every way, but really small.
A few days ago I noticed she gets purple in the face sometimes, usually in the morning. Then she suddenly started losing her balance. She'd sort-of prop herself up with her wing. 3 Days ago she fell over and just layed there until we picked her up. This morning she did it again. She was busy eating and I turned around and found her laying there, eyes open, not moving.
I wonder if it may be dizzy spells? Blood pressure? Most of the time she's perfectly normal, but then she has these moments. I'm really worried about her. She's a very special little thing and we adore her! If anyone had a similar experience please let me know. I'm not sure what to do