This is completely normal. The spinal anaesthetic has to get up to the T4 dermatome (roughly nipple level if you're flat chested) to numb all the bits on the inside that need to be numb for you not to feel pain. There's quite a bit of witchcraft involved in anaesthesia and sometimes the block comes up a bit higher than that. Breathing is controlled by both the diaphragm and the chest wall muscles & so if we numb the chest wall muscles & sensation up to nipple level that makes your chest feel heavy and can make breathing feel like a bit more effort (because it is). However, most of breathing comes from the diaphragm movement though, which is innervated by nerves much much higher up (in the neck) so even though your chest feels heavy and weird your breathing is completely safe (if you think about it, lots of people have thoracic spinal cord injuries, are numb from the chest down and can breathe just fine). Generally if you can move your arms/hands then you can breathe even if it feels weird. Very rarely if the block does come up too high and we're worried that the diaphragm's going to get weaker that would be an indication for converting quickly to a GA to make sure that the breathing is safe - it rarely gets to that point though.
Until the baby is delivered you also have that weight pushing the diaphragm up a bit. After that, for women who want/are able to have skin to skin contact in theatre too, the added 3/4 kg weight plonked on the chest can also make things a bit uncomfortable.
There are some really rare complications of the operation/medical problems specific to pregnancy that can make breathing difficult too, so part of the anaesthetist's job is also to think about those things too, but usually chest heaviness is just due to the spinal/epidural working a treat.
The shaking you describe is pretty normal. Again, it's usually a sign of a good working epidural/spinal! I'm not sure anyone has a really good explanation for it (nerves probably don't help!), but it's just irritating and nothing to worry about.
Tilting the operating table to one side is nothing to do with letting fluids run off the table but is to stop the baby/uterus squashing the big vein that returns blood from the lower body to the heart. If that gets squashed it can make you feel faint/actually faint and is the reason that women are advised not to sleep on their backs in later pregnancy. Once the baby's out we take the tilt off the table.
Nausea/vomiting are common. Often it relates to blood pressure and we do try really hard to stop that being a problem, but sometimes your brain registers that it's changing before the blood pressure cuff does. There are some drugs that we have to use to help the surgeons control bleeding that can make you feel pretty queasy too. If BP is the problem then that is usually easily fixed by drugs/fluids to bring the BP back up again. If it's drug related then bog standard anti-sickness medication may help. HTH.