I'm around cats all the time - I'd take him to the Vet immediately, regardless of whether or not he is starting to show improvement. I don't mean to sound like an alarmest, but Max's behavior is an indication that he is either sick or injured, and I would to want to find out what/why, start treatment - and find out what to do to prevent it in the future!
Sending best wishes Suz- it is so hard when they can't tell you what is going on!
I hope he continues to do better, Suz. I'm sure you are doing this already, but keep an eye on him and make sure he isn't off hiding somewhere and refusing to come out. It is so frustrating when our precious babies don't want us to know they are ill and/or we don't understand what they are trying to tell us.
We have a house full of fur babies at the moment - Our two, a 17 year old kitty (Jasper aka Jazz) and a one year old puppy (Cosmo Edward), and two more doggies (Holly, 12 and Daisy, 10), that belong to my mother-in-law who is in FL with her boyfriend. The fur is flying but thankfully all are currently healthy. They are sending Max thoughts and prayers for a speedy recovery.
Keep us posted and let us know how Max is doing
Sorry to hear this Suz, hope he's feeling better. It does sound odd. This might sound like an over simplification, but do you think maybe he's just "mad" where you just went on your trip? My mom had a Siamese cat as a kid and said they are very temperamental. Apparently the cat would only allow her, her mom and sisters to touch it when my grandfather was away, and when he was home it only would go near him. But I guess the cat was a bit mad with my grandfather if he would go on long work trips (he drove a moving van). Anyway, I hope he's not hurt and feels well soon!
Raisin makes a very good point. My neighbor went on a vacation alone and while she was away her dog developed a bad limp and was so lethargic that her husband took him to the vet to be checked. The limp went away when she got back home. She has to hide her suitcase because he sulks horribly if he sees it.

Your baby may be punishing you for being away.
Hi Suz,

You must be worried sick. I would be if it were my kitty. It sounds to me as though he is injured. A lot of members mentioned kidney/urinary issues. If it is that he will be drinking more water than usual. Is he? Cats only drink water because of illness or a dry food diet. On a wet food diet or raw undehydrated diet they rarely drink water. I hope he is better or gets better soon.
Oh, Suz, this is distressing to hear that your little kitty is not feeling well, out of sorts and can't explain why. I agree with Marley, the cat whisperer, that your kitty should be examined sooner than later.

Perhaps, he ingested something foreign into his system, when he was outside, or he has a puncture wound that isn't visible to humans. Your vet may be able to do some tests to find out why the little one is not himself and acting with such different behavior.

We, too, take our cats to their own room at night, so everyone sleeps better. You are naturally an observant person, as a writer and the Mom of a feline, so picking up on these behaviors, which are not standard and usual for him, is a good way to begin to diagnose that something is amiss. I'm hoping he'll be back to himself again very soon. xxx ^_^
Thanks, everyone -

He was the same today so I took him to the vet. No answers. He seems perfectly healthy (no fever, skin, body, ears, eyes, gums, etc. etc. all normal.)
He not drinking more than usual (he eats a raw food - wet - diet with some supplementary dry food and drinks a very small amount of water). He's eliminating normally (I checked his box). But he's still feeling and acting strange.

The vet noticed the same things I did -- the twitchiness -- and she wondered if he was in pain. But there are no obvious signs of injury anywhere and he's not having digestive problems, so it's not likely to be anything he ate.

The vet gave him some pain medication for now and if he does not improve on that he goes back for some blood work to see if we can get to the bottom of it all. We came home and he went straight into hiding again.
Drinking a "very small amount of water" could be a sign of kidney trouble. The cat will still used the bathroom, but it might be with pain. I had to "bribe" my cat to drink water and even force feed her water with a dropper (and she had already had a saline injection from the vet) for a few days at one point as she was suffering from dehydration but kept refusing to drink. I started watering down her food a lot. A diet too high in protein (is the raw diet mostly protein based?) could be hard on the kidneys too I think. Mine ate wet food too (and some dry until the problems started - then no more dry!). I had to start changing up her diet a lot. Cats water or they will get very, very ill. They can do without food for a few days but not water. Water down his food, skip the dry food and get his blood tested to check the kidneys asap.
Oh Suz - poor Max (and poor Max's mommy!). I hope you are able to sort this out ASAP. Keep us posted, ok?
Hopefully it is nothing serious. If the vet couldn't find an injury then maybe it is not a serious one if it is one? If he is back to normal after the pain medication you will know it was that & not illness. I wish I could hug you but I will just have to hug my kitty instead.
Oh, poor kitty. I can imagine how worried you must be. I have no advice but I have my fingers and toes crossed for the little guy.
Oh I hope they're able to figure something out! That sounds very odd. I was thinking a bee sting too, I had a Burmese (Ninnin) who once got stung and had similar behavior for several days. No twitching though. Took us a week to figure it out, when we saw the dead bee on the window sill. Ninnin used to get very upset when we went out of town, as does Kitty whom you may have seen in some of my posts; Kitty will sulk and pout and generally let us know in no uncertain terms that he is upset about it, both before and after travel, primarily by ignoring us refusing to be near. Monitor the food and water thing closely; when cats stop eating it's generally very bad, and gets worse far quicker than their human companions would like. I hope Max is better soon! It's hard to imagine an unsocial Siamese
So sorry to hear Suz! Did you get any tests done today (standard blood panel/urinalysis?) - or was it just a visual examination?
Suz, I just saw this! I'm so sorry to hear about handsome Max. What a pickle that the vets did not find anything. I also hope they have done some tests. Also second what Aida said: if they don't want food, it's time to start waving some red flags at the vet, regardless.

Has Max ever acted like that before? Our Hank sometimes (once in a blue moon) purrs, hisses, spits, and compulsively rub our legs. We joke that he is psychic or can predict the weather or something, just because one of the times he did that the tsunami hit in Japan. Not sure where I'm going with this idea except to hope that it's one of those Weird Cat Things.
Suz-((( I really hope you'll be able to figure out what's wrong SOON! In the meantime I'm sending extra healing vibes your way. Poor Max-((

Hang in there!
I'm so sorry to hear about your Max. My chocolate Siamese went through a similar phase last year. We think it was something she ate - maybe a bug or something - but she bounced back after a few days.

All the best for little Max. I hope he's back to normal very soon!