Hello,
I am doing both mahasi noting and TMI for about two years now. I have been to a few Mahasi retreats, about two weeks each.
I am a terrible sleeper (Genetically Predisposed I am afraid). During daily life, I use a low dosage of sleep medication about 5 times a week. This keeps me thriving and does not seem to affect my mindfulness during my daily 1 hour meditations.
What is your opinion on continuing this medication during retreats?
I use oxazepam (5 mg) or quetiapine (aka seroquel, 25mg). The latter being prescribed off label by my doctor    to treat insomnia. I take it in turns so not together.
All the best,Peter

JMHO, but if you use it in your daily life then keep using it on retreat. I can't envision a reason why it would be a bad thing to continue.

+1 to what Chris said.  Also seroquel may be having slight mood stabilizing & anti anxiety effects (even if that's not the reason your taking it) that you wouldn't want to suddenly remove while on a retreat.

Oxazepam is a benzodiazipine, sudden stoppage could lead to severe withdrawal symptoms and death. So....+1 on continuing it while you're on retreat. 

Basically, from a meditation perspective it's not at all necessary to stop your meds.

And from a medical perspective, best to talk about it with your provider.  ;)

Thank you all for your answers. I really do appreciate it!
with much metta,
peter