Not only absence seizures or ADD as a possibility here. Also discuss sleep disorders
with the pediatrician. The combination of symptoms
you describe (short attention, dozing in class, anxieties) fits very well with pediatric sleep disorders. My son has this and is completely sleep deprived if he goes without treatment. It makes a huge difference in his ability to cope, although when untreated doctors originally thought he was highly-anxious, atypical ADHD.