I always hallucinate (visually or auditory) to a certain degree before I go to bed. However this did not start with my meditation, I now realize, I just became more aware of it since (as I've slowly become more aware of a lot of things). I think it happens to many people.
(excuse me as somehow I got rambling on this)
When I read people meditating for longer than 2 hours a day a few questions can't help but rise in my mind:
-What kind of life/job (or lack of job) allows you to have that much free time?
-Why meditate for that long? Aren't there other things in your life (hobbies, responsibilities) you want to attend to? If that's what you want; or enjoy then fine; go for it. But if it's causing problems I say it's too much.
While I now enjoy meditation and I miss it if I ever go a day without doing so, I don't desire to meditate for longer than 20 minutes.
I say this because when I started I was meditating for 20 minutes or longer and when I did this for a few weeks I got into a lot of trouble. I was always feeling like I was entering another dimension, had sleeping problems, severe headaches, hallucinations and anxiety. Now that I don't meditate in that way for that long I feel much better.
Most professionals whether doctoral or religious, I read in regards to this recommend meditating for just 5-15 minutes a day, at least to start. I've been doing just that for many months now and am getting into a pretty good feeling routine but also feel like I'm making progress (albeit slowly, that's fine for me) Progress to what? I don't know yet; but I'm sure I'll know more one day

I look at meditation as a way of improving my life; my mind is the vehicle that traverses this life. Life is the experience to be experienced and enjoy. Reading, learning, art, music, games, sport, relationships etc. If some people want to do nothing but meditate all day long; that's fine, but it's not for me. Sure I'd also love to explore the secrets of this universe but not if it costs me my health.
At least in my experience meditation seems to be similar to drugs in that;
-it can create lasting effects, both when done and when/after quiting.
-the amount, type and duration matters a lot.
-setting/surroundings are important
-your present circumstances (both outside and inside your mind) effect it greatly.
I've also had experience with relatives (not myself) who've struggled for years with regulating their medication and had far worse problems than mine in regards to meditation. So if I had to guess (like the other said I'm no doctor so listen to your doctor first), but I'd say medication is likely causing you problems whether it's not enough, too much or the wrong kind.
It's similar with meditation; different types lead to different results (do you close your eyes or keep them open? etc)
One last question that is rather personal so you don't need to answer it, but it is something to think about;
Is your anxiety a mental problem; or is it caused by your life? In other words 'righteous anxiety'? What I mean by that is; for example if someone's job is extremely stressful this naturally causes anxiety. And the best solution to this problem is not medication or meditation; but to get a different job. If that's not possible then obviously you must deal with it and these other solutions are necessary.
This is a complicated issue and could be discussed for hours. But I've noticed in my short lifetime that the amount of anxiety seems to be ever increasing in my society (America) and in large part seems to be due to people living in ever increasingly poor living conditions. (Demanding jobs, lack of sleep, side effects of chemicals in meds and food; over reacting to problems, the list goes on). DESPITE the fact that actual opportunities have improved (technology, communication, people's emotional capacity, laws and rights etc.)