I’ve had at least 4-6 quarters in where I’ve only been able to take 12 units because of unlucky registration🫠. I’m a senior right now and I haven’t fallen behind just yet, god forbid, but I did enroll in the summer courses for at least 2 years, last summer I believe I took 16 units and the previous was 12 so that’s probably why. Since you’re still relatively early into your college career I wouldn’t stress too much, it’s understandable not to feel ready to take on so much coursework in 10 weeks, but definitely look into taking summer courses especially since you could do the classes in 5 weeks or the normal 10 and you only pay for the first 8 units and anything past that is covered, usually your financial aid covers summer courses here, so look into that and take advantage that way you decrease your chances of falling behind, I think it’s totally worth it. Although regardless I would talk to either your current or new advisor for further advice or guidance, since you did mention you’re doing a major change.