fussy baby having trouble sleeping after traveling

My close to 6-month-old baby used to be happy, calm, independent, smiley, and very regular in his habits. An easy, delightful boy who would charm everyone with his smile and disposition.

Then 10 days ago, we went on a car trip to a workshop and stayed for a week in a town at 7200 feet. The travel took close to two days one way. As soon as we arrived, our baby could not sleep. Calming herbal teas and over the counter combination sleep remedy didn't help. He appeared calm but turned his head left and right startled at the new surroundings.

Unfortunately his regular nap schedule was disturbed due to the trip's workshop activities. At night, he had a very hard time falling and staying asleep. He had nightmares and cried a lot in his sleep. My husband and I had to take turns sleeping with him in our arms or taking walks outside.

About 6 or 7 days ago now, I gave him Arnica 200c in 3 doses every 12 hours for the trauma. The arnica helped a lot with his mood and a little with his sleep (he stopped having nightmares and crying heavily). Still, he continued waking up more and more often as the night wore on. My husband thinks he might have had a headaches from the high altitude and trouble retaining body heat.

Eventually, by the 7th day of our stay, he still woke up 4-5 times a night, more often as the night wore on, but he no longer cried hard. He just had to be held to sleep from about 4 am till 7 am, when we got up.

The 2-day car trip was also very difficult. He was cranky, grunted in discomfort, couldn't settle in the car seat, and overall wanted to be held in order to calm down or sleep.

When we got back home 2 days ago, I gave him Chamomilla 30c, 3 liquid doses yesterday and one this morning.

But he continues to be fussy much of the time, one minute he is cranky, the next minute he laughs and shrieks in joy--although these happy moments are brief. He gets exasperated or irritable when playing with his toys.

At night, again, he wakes up to eat the first two times and goes back to sleep. As we approach 4-4:30 am, his sleep gets very shallow, he wakes up often, and he cries in his sleep a little, and eventually he needs to be carried and held until the morning. This morning, he actually seemed more cranky and irritable that he has been--I might have inadvertently caused a proving of the Chamomilla.

During the day, he needs to be carried for extended periods of time in order to take a nap or to calm down. During the naps, he occasionally cries. His body temperature is on a cold side, and he has a little cough that seems to be caused by tickling in his throat.

Please help! The parents are not getting any sleep, and we want our delightful, happy boy back. Thank you in advance for your help.