This is going to be very long because I seriously feel bad for you. There is a summary at the end if you don't wish to read it all.
You haven't made yourself silly as he isn't in your head and doesn't know what you are thinking. Men are generally clueless when it comes to picking up signs. He doesn't know you sent the card with a crush and a hope for more. If the card was polite and friendly with nothing suggestive or flirty in it then you haven't disgraced yourself. Professionals (medical or not) who help the public do get cards every now and then. Sending it to their work address rather than personal email, sending them an appropriate polite card rather than something saucy or a naughty photo or text is all normal and happens without anything inappropriate intended by it.
As a general point, I will say that people can and have called or sent a text to say I got your flowers or card, thanks very much I loved them and so on. So I don't agree with no thanks for the thank you's. Most people don't though because thank you cards are usually sent in a formal or old fashioned context and the recipients tend to be either old fashioned too so will not want to make a big fuss about it and will be keen to minimise and move on or will be the type who gets so many thank you cards it's impossible to personally acknowledge each one.
Setting aside that there are professional boundaries, a brief telephone conversation without additional charge is part of good customer service. It's a personal touch that gives the patients the impression that their medical professional cares about their wellbeing and is the type of customer service or bed side manners that will get his patients recommending other patients to him particularly if this is a private treatment not an NHS one. A private medical professional is more invested in getting and keeping patients returning because they aren't getting the NHS steady stream of referrals, they have to do more 'schmoozing' to keep and attract patients.
Moreover, him saying it's good to see you is just polite pleasantry. Even if he genuinely thought it was good to see you, yeah it's good to see you £££ and your money back. It's nice to have a patient come back instead of go see someone else particularly as you are paying and have more freedom to move and change practicians since you are paying privately so it's a compliment that he hasn't totally fucked up, that you were happy enough with his service and clinic to return and that he is going to be making some more money.
My advice to you personally is to be honest with yourself about what area of your life are you escaping from with these thoughts and fantasies about an inaccessible person. You know he is highly desireable (status, looks, social standing, money..) and his approval of you would make you elated and temporarily allay any insecurities or fears you have about yourself. If he can like you, then you are good enough and any other man can like you. If he likes you back, then you won. However, when the dust settles you will see that there was a power imbalance and that him crossing the professional boundary, even though it was with you and you are doubtlessly a genuine, decent woman who felt a real spark, you will later come to wonder how he managed to do this despite his years of training and the issue of jealousy about him getting close to female clients will surface. You will not be able to trust him. Even if this doesn't happen the second likely scenario is that you do date and then for whatever reason he might cool things off or break them off and then you will be sitting there seeing the events in a whole different shade: he used me, he misled me, he behaved unprofessionally, if he does this to me, how many other women has he manipulated? And you would be tempted to go the legal route to punish him for slighting you with any perceived deception even if you aren't normally vindictive. Why? Because you two wouldn't have started on equal footing. In codes of ethics they say it's frowned upon and discouraged. They aren't doing it to spoil your fun or stop 'soulmates/twinflames' from getting together. It's there because Medical councils and professional tribunals have seen this scenario time and time again. It might end well for the 1% and that was before #metoo and online media outlets in general. Things like this could ruin a career. The medical community is surprisingly small in an area and everyone knows everyone, word going around wouldn't be good for his reputation, even if it's been a while since you were his patient, basic question of: so how did you two meet? Are you going to lie to everyone about how you met?
See it from his side, this is something he spent years working towards, this is possibly his own business. This is his livelihood, his career and potentially his identity. He sees good looking and sporty women regularly at work let alone in his, doubtless, healthy lifestyle and hobbies where he mixes with sporty good looking women who are FAR FAR safer option to date. Why would he risk all this for you? If this is an earth shattering connection, he would have already said or done something about it but I'm sorry, this is only from your own side as he hasn't said or done anything beyond what a friendly privately paid medical professional would do.
If I were you I would be glad I didn't write anything embarrassing in that card, I would not go back again and look into making big changes in my life that are leading me to fantasise about an unavailable man out of bounds. Maybe you need to date and meet more nice, attractive men who are kind and caring and a regular physio meeting with someone who is those things made you feel great but this isn't about him, this is about you escaping in him and needing a mate with the qualities he displayed.. and remember, just because he is nice at work doesn't mean he is nice to his family or in his own personal life. You genuinely don't know the man. He hasn't even mentioned his marital status, there is literally nothing that hints he was interested in more. And even if he had mentioned it, some people are just chatty.
Lastly, and this comment probably in gest but I will say Physiotherapists in particular are used to seeing women in sportswear at their appointment. Often these days it's tight and fitted such as leggings. Many women go to supermarkets, school run and do their errands in leggings. Tight clothes are hardly a come on these days. Now if she was wearing a super short bodycon dress with cleavage of 3/4 her breasts to the physio appointment then maybe.
To summarise my huge essay, he was just friendly and a polite thank you card is fine. Reassess your life and make some serious changes as escaping in inappropriate fantasies can be a sign of maladaptive behaviour.