Escaping side control is one of the things that people struggle with in grappling. It's not easy. One of the biggest things that makes escaping side control difficult is addressing it to late. It is much easier to escape side control or positions like it if you begin your escape as soon as you realize you've lost position. When you are just beginning your escape after your opponent has already established head control and flattened you out, your journey back to a comfortable position is by nature much harder. So the first step is recognizing you have a problem. If you recognize the problem, then you can go about solving it. There are many types of side control and many escapes for each one, but the overarching goals are keep their weight off of you using frames, keep your limbs protected, and remove one of your shoulder blades from the ground. The theory is much more difficult than the practice, so it will probably continue to frustrate you throughout your bjj career as you find people who are better and better to train with, but just working on those three things will lessen your suffering and make you much harder to pin down.  

That's a real question, and if you have a response I'd love to hear it.
When I think about grappling, I prefer larger interconnected concepts. Ex: An armbar functions the exact same way no matter the position. So I now know that if I find myself in a position where I have my opponents arm straight an armbar is available. Not everyone is so abstract, many people follow linear progressions, it is the base of the 10th planet system, chaining and understanding what the next steps are following each reaction. There are pluses and minuses both ways, and how I understand BJJ has been sort of atypical at the places I've trained, but it also simplifies things when you have the pieces together. In either instance a solid fundamental base is necessary for the success of the system. In my mind, there are less than 20 ways to submit someone, but within those 20 are countless variations, the same goes with takedowns, sweeps, and passes. What you have to do is very simple in most cases, but how you do it is the complicated part, and if you understand what you're trying to do, you can sort of make up how to do it.

I've been thinking a lot about sweeps from the up/down recently and realized that there aren't very many that exploit balance sideways. The majority of sweeps for an opponent standing above you either take them over you (tomoe nage) or drop them to their back (sickle sweep). There are absolutely some examples of sideways sweeps on a standing opponent, but they're few and far between especially moving into no gi. My opinion is that the structure of the position does not allow for the same sideways kuzushi mechanisms as when both people are standing or one is kneeling in the other's guard. Therefore, because it's more difficult to control the lower body base points, more sweeps function to eliminate them entirely, which leads to more forward/backward, push/pull sweeps. It's very much a theory, but it is interesting to me. What do you think?  

When you're seated or on your back and your opponent is standing above you, this is what I call the up/down position. I'm not sure where I got that from, I know it's not something I created, but I don't hear it that much, so sorry to whoever I coopted that from. Anyway, this is a strange position, because it's used across all facets of the Jiu Jitsu spectrum, but not really the same way across any of them.
Sport BJJ- if you wind up in this position in sport BJJ or pure grappling situations a sit up guard is usually the best course of action without established grips, then once you establish grips, you can return to a supine position to launch attacks or continue forward to wrestle up. Remaining on the ground without grips leaves easier avenues for both leg locks and passing as far as your opponent is concerned.
MMA- When we look at the up down position in MMA, it would be unwise to approach the situation by sitting up as there is a high risk of being struck. It is unlikely that the upright person will dive on a leglock as the consequences of giving up top position are greater, allowing us to protect ourselves by keeping our feet in the air, you must continue to fight for the whole round, and usually there is a limit on how much time the referee will allow this position to go on as oftentimes it creates a stalemate. I feel like this unique set of constraints almost negates this position in MMA, although being able to do it well would definitely be an ace in the sleeve of a BJJ based MMA fighter.

Self-Defense- This is an interesting one because if you find yourself on top, you no longer need to engage, but if you are on bottom, it is imperative that you act swiftly and violently. In a setting devoid of rules, if I end up on the ground, my immediate goal is to get back up by any means necessary. That could be strikes, submissions, sweeps, whatever gets me off the floor and able to disengage most quickly is what I need to do. 
*LEO's exist in this area, but in an even more unique situation, because you need to apprehend the other party in this scenario. If you'd like to discuss this further, I welcome you to my cop class at 3pm every Friday.    

I always hear John Danaher saying if you can see the back, you can take the back. It is both that simple and incredibly difficult at the same time. Since part of the work is already done for us, let's leave turtle out of this discussion and focus on the types of back exposure that begin from head on positioning.
Opponent is supine:
When our opponent is on his back facing upwards, there are three ways I can think of that encompass the majority if not all of the ways to take the back. 
Force to one side or the other: this one is fairly simple, and can be a result of our opponent turning to their side to escape or of a conscious decision on our part to funnel them into a back take. Oftentimes, this is aided by the giftwrap head and arm control and a wedge with our shin to scoop them into the control position.
Shoulder exposure: there are two common ways that come to mind when I think about back takes where the shoulders are exposed to achieve the position. The classic stand 'em up sit 'em down from north south and the "vortex" position in both instances we take the back by lifting both shoulders from the ground first to set our hooks.
hip exposure- This is the back take that gets the cheers, utilized in positions like the truck, rolling back takes, or chained off the double under hook pass, elevating the hips from the ground and setting the hooks in is highlight reel worth stuff and proven to be competition effective.

What if we are on the bottom?
I've thought about 4 major ways that back takes from the bottom happen.
Chest to shoulder: It's classic, it works. We drag their arm across our body, pin their shoulder with our chest and begin setting the hooks in. Arm drags and off center closed guard attacks are great examples of the chest shoulder back exposure method.
Underhooks: Another classic, anytime you can achieve underhooks from a bottom position, you can threaten to take the back. 
Armpit to armpit: It almost seems like an accident, but there are whole instructionals about octopus guard and lots of footage of people getting their back taken by understanding back takes with an armpit to armpit connection.
Chair sit: A move for the cool kids, kiss of the dragon, matrix, deep 1/2 they all have a version of a chair sit back take. Once you've gotten mostly behind your opponent, connect somehow to their hips, exploit their balance using your shins, and sit them down to place the hooks.
A very simplified overview of back exposure options, if you have one that you feel doesn't fit within these parameters, I'll happily add it.