Should I be the one who is upset or is my boss the one who should be upset?

Yeah, if I were you I'd be upset - so much that I'd be looking for a new job. You're taking a couple days off for major surgery and all they can think about is a bid deadline?

There are really only 2 scenarios I can think of, and neither one is good.

1. Your boss is selfish jerk who only cares about maximizing profit and doesn't care about you one bit - except to the extent that you can help them make money.

2. Your company is so thinly staffed that you're the only person there who can prepare and submit a bid. This would indicate that the company is small and/or too cheap to hire more help. Its unavoidable when a company is small and new, but no company should be in a situation where one employee being absent leaves them unable to complete their projects on time.

After you cool down a bit think through some solutions. Can you reschedule the surgery for after the bid submittal without jeopardizing your health? Is there someone else in the company who is capable of handling this bid? Is there a way you could work overtime and finish this bid before going in for surgery?

Present a solution to your boss, then let your boss know that after 8 years at the company its very concerning that they are so upset about you needing a few days off for a major health issue. Discuss the idea that they should hire more people who can do bids or spend more effort training existing employees to cover for you so that the company isn't completely screwed. What if you had a heart attack and were suddenly in the hospital without notice? If your boss can't recognize that her reaction was wrong and admit that they need more people or better training so you can be absent once in a while, then its time to start thinking about your career beyond this company.

Since you had a choice, of two different dates............you should have discussed this with your boss.  However, if you do NOT tell her there was a choice - then she has no choice but to accept it and move on.

You might have informed your boss that you were waiting for a date for surgery, but that's where your obligation ends. If you had a medical EMERGENCY, (i.e. broken arm or leg, heart attack, etc.) do you think your boss would have a right to be pissed off that you didn't TELL her first?  No. 

You can apologize for not giving her more notice, but honestly--your health IS more important and you should not feel bad for thinking so. You also can't schedule your health concerns around someone else's schedule and your employers. You can be hurt and pissed. Just don't retaliate or start bad-mouthing the boss--that won't get you anywhere. And keep your stress levels low before you have to have the operation. 

Ignore her outburst. And you may indeed be back to work Monday. 

You should have communicated with your boss before finalizing the date. BTW, I was up and around 24 hours after having 1 stent inserted a couple months ago.

You have reason to be upset, but try to just let it go.

Neither of you handled that well. She's treating it like an elective surgery, so it's possible you did not explain the necessity of it quite as well as you might have.  If you did, then she's being a jerk. Do as much work as you can on the bid before you have your surgery and the leave the project for her or someone else to continue to work on.

Skip the stents and have a  heart attack. That will show her.