Help! I am SO Tired!

What is happening?
Carson has been sleeping through the night since about 12 weeks thanks to "On Becoming Babywise". It has been a dream.
Things are changing!
Since the night of his birthday he wakes up several times a night, screaming at the top of his lungs and not able to catch his breath. We rock him back to sleep but the moment you lay him down he cries again and reaches for you, becoming hysterical.
Sunday night this went on from midnight to 4am. The next night it went on for two hours and then we let him cry it out which took another hour and was distressing.
Last night was the hardest though. He woke up at 10pm and I rocked him for an hour. I went to bed relieved. A half hour later he was up again. I rocked him for 30 minutes, trying to lay him down several times. He acts scared of me leaving and hides from the shadows on the wall. Finally, back to sleep. At 2:30am though he was crying again. I was so tired I broke my rule; I brought him into my bed.
The next four hours were him crawling on me trying to get comfortable. If I even laid him beside me he would scream. He had to be right on top of me, preferably with his head nuzzled under my neck and an elbow in my 'milk makers'...very comfortable let me assure you. He did at one point give me a kiss and hold my hand to reward me for my patience.
From what I am reading online and his very attached actions lately, I think he is going through separation anxiety???? Experienced moms, what do I do??? I need my sleep.