Hello, this is Dr. Linda. I hope I can help with your question today.
I assume that you are not too worried about Motz shedding. Regardless of where you live in the country & how cold it has been there, the days are getting longer & that is the stimulus for animals to start shedding.
If the weather has been warm, it is perfectly normal for a horse to lie down & nap. But if this is totally out of character for him, this could be a sign that he is having some discomfort, either belly pain from colic, or foot pain from impending founder.
If you observe him grazing in between his down periods, then it is unlikely colic, or he just may be experiencing some gas pains. If he seems comfortable on his feet, does not stand with his front feet well out in front of his hindfeet, then hopefully he is not trying to founder on you.
If you feel comfortable taking Motz's temperature, that would be helpful. Anything from 99.9 F up to 102 F would be normal. Over 103 F is elevated & he may need antibiotics.
Otherwise, do not feed him anything but grass hay for a couple of days. If he continues to eat, does not appear painful on his feet, & seems bright & cheerful, then slowly reintroduce his alfalfa & oats over a day or so.
If he continues to lie down & especially if he wants to roll, call your veterinarian ASAP.
I hope this makes sense & has provided you the information you needed. Please let me know if you have any further questions or concerns.