My first three I co-slept (baby in bed with me, snuggled in my arms). First baby was an awful sleeper. Sometimes she would wake every 30 minutes through out the night. It's torture to not get enough sleep! She did start sleeping a bit longer as she got older, but she still woke up every 2-3 hours until she was THREE YEARS OLD. Then she seemed to adjust and sleep better. She was on thyroid meds, so I think that might have affected her ability to sleep.
Baby #2: He always slept pretty good. He'd go 3-4 hours straight. It was awesome. He didn't start sleeping through the night until his molars came through. Actually, he's four years old, and he's just now starting to really sleep through the night. Prior to this, we'd put him down in his room (when he got older, we put him in his room in his bed, along with his sisters). In the middle of the night, he always came in and slept on a little bed on the floor in our room (no room in the bed with us!). My oldest did this too. They each had spots on the floor. I realize that might sound crazy, but it's worked for us! We don't mind them in our room, and for us it works just fine to have them there if they are scared. Just in the past few weeks we put their little beds away (in our room) and now they stay in their room all night. They do great.
Baby #3: She also co-slept. She slept similar to her brother, only she would sometimes go stretches of 8-12 hours of sleeping (this was when she was a newborn. She didn't do this older.). She goes to bed in her bed and comes in our room at night. Other than that, she sleeps pretty solidly. She quit waking up around age 2.5 yrs (she'll be 3 in a couple weeks). It was when her molars finally cut through that she slept much better.
All three of these went through phases of sleeping much worse during the night, depending on what type of mental growth they were having. Often the baby sleeping spells started at around 7 months. Sometimes they would wake up for a few hours, SUPER happy, and SUPER awake. Looking back, I realized I let them nap too long during the day, not giving them enough need for sleep at night.
Baby #4: I tried to co-sleep with her. It was so bizarre! As a newborn it worked great. Then when she got older, close to 4-6 month-ish, she would fall asleep in my arms and wiggle, wiggle, wiggle. She would never settle. It kept me awake almost constantly. So, I decided to lay her in the co-sleeper next to our bed, and she settled and slept great. I was a little surprised. I kept trying to co-sleep with her in my arms, but she kept wiggling and never really settled. It was keeping me awake. So, I put her in her co-sleeper again. She'd settle and sleep great. It became really obvious, really quickly, that she slept much better in her own space. I didn't know babies did that! I ended up getting prego when she was six months, and I needed sleep. My baby would wake up when hubby got up in the morning, so I moved her into another room. Now at 12 months, she sleeps solidly through the night. I have NEVER had a baby do that. She seriously sleeps almost better than all of my other children, excluding my 8 yr old...or maybe even better than her! It's a blessing since I'm prego and NEED more sleep than usual (and the others still regularly wake me up randomly).
So, each baby is different. I did notice a similarity that once they finished teething (mine finished cutting their 2 yr molars around age 2.5-3 yrs), they slept better. They still woke up, but if they were in the room with us, they were fine and went back to sleep - taking no effort from us.
I am loving that my 4th baby is sleeping through the night (though I'm sure she won't tonight since I am writing this!). I do miss cuddling her at night, though. But each baby is different! She's a very cuddly baby overall, so I get my snuggles during the day:-)
It WILL pass one day!